I have one Bachmann Engine that came with a sound value decoder which I intend leaving in that engine, at least for a while. And that is the USRA Mikado.  The only reason I would do that is that two of the whistles in there are very beautiful sounding and pleasing to me, and both of been dropped from the Soundtraxx library.  They are the Southern 3 chime and the Crosby 3 chime.  Whistles by those names appear in newer Soundtraxx decoders, but they are not the same sound, and not as nice to my ear.

Most often used behind large shops to save space otherwise taking up by many multiple switches to service all the shop tracks.

Bachmann used to provide in certain engines an incredibly stripped down sound decoder called "sound value."But I don't believe it was offered for sale separately.

These typically are replaced by sound – oriented modelers with more advanced decoders and may be for sale cheap on eBay, Check.

If you are unsure about painting and ballasting track, practice on a couple of loose pieces first.  You can try different colors of brown. Some people spray the track gray first, then paint the sides of the rails with a rust marker that's available, then wash-paint individual ties different shades of browns to show individual weathering.

Try any of this out, and I guarantee that you will never be happy with the appearance of plain out of the box track again.

I don't find the appearance of grey plastic roadbed acceptable.  If it was mine, I'd spray paint the whole thing a mid-brown first, then add ballast. 

There are many different theories and ideas about how to paint track realistically since none it is  realistic the way it comes.  Some people mask off the rails or the ties and paint them separately, and some go as far as painting ties individually. I don't have enough time left on earth to do all that. The CSX main line track about 200 feet from my house, the rails and ties are almost the same brown color. Which probably comes from the rust washing down on the crossties from our frequent and heavy rain down here on the Gulf Coast. That's good enough for me. Spray painting the track with brown blends with the Browns and greens of the adjacent scenery very well.  It also ties together different brands of tracks like Bachmann and Fleischmann.

I never, never, ever, ever unplug the locomotive/tender wiring. Why would you want to? If it's a storage issue, keep the engine on a shelf somewhere.

And if a wire pulls out of the plug, the only solution is to replace the plug itself. Professional techs who do this work tell me other aftermarket plugs are preferable.

If you replace these items, you have to know which wire is which. The NMRA has color coding guidelines, but Bachmann apparently does not follow them. So you have to backfeed each wire to see what is what on both engine and tender. If this is your first steam engine and you're asking these questions, you certainly will need to have plug replacement done professionally.

All of the above applies to engines equipped with DCC. If this model happens to be a very old with a single wire, it might be easier.

HO scale trains are very different than the old fashioned larger scale toy trains that used to go around Christmas trees.  They are more delicate in every aspect you can name. Nothing can stand up to the abuse and crude handling that Lionel an American Flyer Trains took it in stride.  The least little irregularity in track will derail the train.  Mechanisms have much smaller parts that can chip or break in any of multiple places very easily.  I received my first HO train set when I was 12 and it went immediately onto a plywood table. But I knew people who got similar sets who tried to set them up on carpet and they could never stay on the track, and got boxed up and put away fairly quickly. Good for me because I bought most of that stuff from them cheap.

That's great. The only issue you should have is easily corrected, getting the railhead heights lined up correctly.

Is this the Fleischmann track design for three rail operation?  With the third rail in the form of little metal studs in the middle of the ties. If it is, won't be a short circuit with the track switch is installed?

If you are buying a new three-way switch, it might be less of a gamble to buy an Atlas item and shim up the cork roadbed to match the Bachmann track.

Very cool! The power of the Internet!

You can always cut a notch in the roadbed to run a wire under.

Who is PM?

Youhave two Shays now?

You can always spot the old one out behind the back shop like it's being repaired.

Sacrificial donor engines are the order of the day in today's Model Railroading.  The days of American manufacturers carrying every possible spare part forward into infinity are long gone.

You might buy an undamaged engine and keep the present incomplete one for parts.

Real railroads do this.  Union Pacific's famous 844 has been kept running for over 50 years by the presence of sister 838 in the Cheyenne Roundhouse, which has slowly been cannibalized for everything under the sun for the whole time. At this point in time there's not much left of the 838, but I'm pretty certain that eventually the 838's much less worn frame and running gear will be reinstalled under the 844, at which time the 838 will no longer exist.

And throughout the steam era, older engines were often kept in deadlines at the shops for this exact same purpose.

Call Soundtraxx customer service.  The leaders in the business.

https://soundtraxx.com/

If you are asking this question you probably should consider professional installation.