I advise you to clean the tops of the rails of your tracks before you try to use them, because the amount of surface oxidation that can interfere with train operation is not visible to the unaided eye.  Either steel or brass sitting around for 25 years, even in a sealed container, will almost certainly have a bit of oxidation on its surface.

Just get a piece of tightly woven cloth, such as a piece of an old sheet, put a little mineral spirits on it, and rub the tops of the rails with it.  Mineral spirits makes a better cleaning solution than something like alcohol, because it leaves the metal in a condition that is slower to oxidize again.  Keep cleaning the top surface of the rails until the cloth looks clean when it comes off the rails.

Then, clean the surfaces of the locomotive wheels what come in contact with the rails, so that they can pick up the electric current to turn the motor in your locos.

There are conversions to MicroTrains magnetic couplers that use the same coupler box as the old style ("Rapido") couplers that you have now.  They have a different configuration inside the box than the regular MicroTrains couplers, and often do not work as well as the regular MicroTrains couplers because the configuration inside the box tends to let them sag outside the box.  But, it is the easiest conversion, especially if the couplers are mounted on the trucks instead of the car bodies.

It is also possible to remove the box and replace it with magnetic knuckle couplers and boxes from MicroTrains and other manufacturers.  That is somewhat harder, especially if you are talking about truck mounted rather than body mounted couplers.

The easiest way to replace truck mounted Rapido couplers is to get new trucks with magnetic knuckle couplers mounted on them, but that is also the most expensive approach.

Look here for the "parts diagrams" for the 4-6-0 loco and tender: https://estore.bachmanntrains.com/index.php?main_page=index&cPath=70_578&zenid=6ucfh7lo2cob013vg9nhh7cer1

Somebody else will have to tell you the decoder info.  On the programming track, the first thing that comes up is the manufacturer number and then the decoder number.  But, those are pretty much Bachmann numbers, rather than something you would recognize from decoder manufacturers.

There are several recent Bachmann models that have  never had parts listed for sale by Bachmann on their site.  There have even been questions on this forum asking when parts for those new models would be listed on the Bachmann site, but "The Bach Man" has never answered those questions.  So, apparently, whoever is the designated "Bach Man" is either not told or not allowed to tell us which of their products will or will not eventually have parts sold separately.

If you are one of the unlucky ones with products that have no spare parts listed, I suggest that you call Bachmann's repair facility on the telephone and ask them if they can repair the item or maybe send you the parts.  I have had some luck doing that. As their website says:
"Bachmann's Service Department is available Monday through Friday from 8:30 am to 4:00 pm (All Times Eastern). Customer Service for all scales can be reached toll free by US and Canadian customers at 800-356-3910 or Fax at 215-554-6734. Customers from all other countries should call [Exit Code]-1-215-533-1600."

Look here: http://estore.bachmanntrains.com/index.php?main_page=index&cPath=66 .

If the couplers are not at the same height when the cars are on a level track, then you really need to address the couplers. 

Microtrains sells a coupler gauge that sits on the tracks with a MicroTrains coupler in it that is at the correct height.  There is also a trip pin gauge (flat piece of metal 0.010" thick) that lets you figure out how to make the trip pins be at the correct height once you get their couplers fixed.

There are a lot of knuckle coupler types and mount types, made by different manufactures, and even the same manufacurer at different times in the past.  And, there are the conversion knuckle couplers to get from the old Rapido type to some sort of knuckle type.  Those conversion types typically have a T-shank inside the coupler box and they have a tendency to sag too low at the knuckle.  So, without seeing what you actually have that is giving you trouble with your trains uncoupling, it is hard to tell you what you need to do to fix your specific problem(s).

 A 2' wide layout will only allow you to use about 10" radius curves to turn the trains at each end for a continuous run, assuming you allow a 2" (from track centerline) buffer around the outside of layout to keep trains that jump the track from also jumping the layout and falling to the floor (or ground). 

Although there is sectional track down to 9.75" radius, and a lot of N scale equipment is designed to run on that tight radius, it tends to look pretty toy-like when going around such a tight bend in the track, and some of it really doesn't do so well mechanically at that tight radius.  Only the 0-4-0 "Docksider" switcher looks realistic on such tight curves. And, of course there are trolleys, too.

So, most people who are limited to 24" width either make a "switching layout" that does not allow continuous running, or a tight loop, with about 2' of straight section between the 180 degree turns at the ends of a 4' layout.  In the tight loop, there is a bit of room inside for some switching on a diagonal, but it is hard to connect the two sides of the loop diagonally so that the direction of the trains can be reversed.

If you can afford a slightly wider layout, then you will have a lot more options on track plans and equipment you can run.  By the time you get to a 30" wide hollow-core door (HCD), you can use 12" or 13" radius track.  There a lots of track plans available for HCDs of various widths.

The number of cars your engine can pull is easy to determine by simply adding cars and running the train around your layout.  When one more car causes the train to stall or derail by stringlining, you know that you have one too many of those cars to make it around your layout.  

But, not all cars are equal in their resistance to motion (drag/friction), and different track arrangements (curve radius, "S" curves, grades, etc., etc.) create different amounts of drag in various areas of the same layout, with the limiting configuration differing from layout to layout.  So, it is difficult to get exactly the right number for the maximum number of cars on your layout by asking for that information on the Internet.  At best,  you will get something like "My XYZ locomotive can pull 15 of my [Bachmann or Atlas or whoever's] hopper cars up my 2.1% grade." But, your results might be substantially different with different cars and a different curvature, even on the same grade.

One other point that is important: if you run your train for an extended period of time with the maximum number of cars that can make it around your layout, you will probably have the traction tires come off you locomotive, if it has them.  The problem is that you are most likely having the locomotive's wheels slip on at least one part of your layout, and maybe a lot of your layout if it is flat and has large curves.  The train keeps moving, so you need to try to watch for the wheels to slip.  That is a lot easier to do with steam locomotives than diesels, because you can watch the valve gear moving on the steamers. And, many diesels don't have traction tires, plus they are easier to replace on the diesels that do have them, compared to replacing them on steamers.

This forum does not appear to offer a members' "for sale" section, so, apparently, not here.

Some other model railroad forums do offer members a sub-forum to sell things: "Swap Meet" on the "Trainboard" forum https://www.trainboard.com/highball/index.php?forums/trainboard-swap-meet.151/  and "Trading Post" on "The Railwire" forum https://www.therailwire.net/forum/index.php?board=12.0 .  But, you have to join those forums and make a specified number of posts before you have the privilege of posting to those subforums.  But, joining other model railroad forums is a great idea, anyway.  They are free to join, and they provide a wealth of information and advice that is not found on manufacturer-specific forums like this one.

And, of course, there is eBay, where buying is easy, but selling takes more effort than those model railroad forums.  I get a lot of my stuff from eBay, including things that are no longer still available from Bachmann.

There is a lot of track with 9mm gauge available all over the world. 

The United States has a real railroad standard track gauge of 56.5", so models of U.S. railroad equipment are built to 1/160 of the real size to run on the 9mm track, which is "N gauge" (for Nine millimeter) gauge, and it is called "N Scale."

Some other countries have different track gauges for their real railroads.  So, to use the same 9 mm track, they end-up using slightly different scales, but still call it "N scale."

That might make a slight difference in the size of your old model compared to your new model.

There is another possibility.  The model might be really made of a narrow gauge locomotive, which might be something like a real 42" or even 36" track, with the model designed to run on the same 9mm "N gauge" track.  That would make a very large difference in the actual model size, and most of us would not call that "N scale".  But, who knows what some toy maker decided to call something a long time ago.

The PowerCab should be able to run 2 DCC sound-equipped HO locomotives.  It has a current rating near 2 amps.

From the descriptions that have dribbled into this thread, it sounds to me like a short circuit in one locomotive, and it sounds like it is being caused by the pickup in the loco being opposite the pickup in the tender.

Not knowing the particular locomotive, I have to ask: Are you sure that the plug on the cord between the loco and tender is not up-side-down?

Without a better description of what/where the turnouts go/connect trackage, we really can't help you very much.

For example, if the two turnouts that "go to the right" are making a path across the inside of the oval, then you are creating an electrical short circuit, because the rail that is on the inside of the oval on one side ends-up connected to the outside of the oval on the other side of the path across the oval.

Similarly, if a turnout leads into a loop, where the track from one path through the turnout comes back to the other path through the turnout, the same thing happens with connecting the two rails together at the turnout, an an electrical short circuit results.

When you get a short circuit, most controllers have a circuit breaker that disconnects track power.  You did not tell us what type of controller you are using, so we don't know what type of indication your controller might have that it is experiencing a short circuit.

However, there are other possibilities besides short circuits, so you really need to tell us more, or we can't be much help.  Please describe where your turnouts go when they leave the oval and also tell us what controller you are using to power the track.

You will have to tell us what your track setup looks like when you have the turnouts included.  It sounds like you might have a short circuit created by some sort of loop or wye in your configuration.

Bach-man,

When you say that the parts become available through the "parts department" as soon as the models they are on become available, are you saying here: https://estore.bachmanntrains.com/index.php?main_page=index&cPath=70&zenid=mflits0km59vlmv0acd5i5r693 ? The last loco to list parts there is the K-4 Pennsy 4-6-2.  Which came out after the sound version of the 2-8-0.  And, the latest sound version of the 4-8-2 has been available for a while, but there are no parts listed for it on that website.  So, it seems that what you posted is incorrect for 2 of the last 3 steam locomotives.  That is why we are asking the question about parts availability for those 2 locomotives.

So, if you are able, please check with whatever powers at Bachmann corporation really know if/when the parts will be available for the new sound versions of the 4-8-2 and the 2-8-0.

Bach-man, your posted "reply" was not actually a reply to the question we asked.  Please read the questions again. 

The issue is whether the extra parts that you get when you run a new locomotive will be made available to us customers through the Bachmann Parts Store, and, if so, when for the new 4-8-2 and the "After 2017 version" of the 2-8-0, both of which now include sound.