If you include photos or a discription of the couplers, we might be able to help you.  Each company makes their own different style of coupler, so a photo would be helpful.

Steam would have to be a Lima Shay


Diesel would have to be an Alco RSD-4 (#201 in the photo)

KCC #201 is the last RSD4 in the world, now located in Snoqualmie, WA.

Electric would have to be a GE EP-2 Bi-Polar

Well....lets see....

1 Bachmann 4-4-0
4 Bachmann F7
1 Bachmann B23-7
1 Bachmann Trolley
1 Life-Like BL-2
1 Life-Like GP18
4 Model Power GP40
1 Atlas GE U25B
1 Atlas GP40-2
1 Atlas 0-6-0
1 MRC Alco RSD15
1 Trix F7

If your shays were unlettered and brand new, then there should be a bag of parts included that have different bunkers and stacks.
As for the K27 parts, a bag of parts are in the works from what I here.

True, Bachmann has not produce many Colorado specific models, but other model companies have.  I agree that there should be some other narrow guages models produced such as the White Pass & Yukon.  WP&Y had some pretty interesting equipment that I think would be popular, but nobody makes it.  It is kind of a shame.

Kadees are okay from what I hear.  The only problem with them that I see is that they have no drop pin, so to uncouple you have to use something like a flat blade screwdriver to separate them.  Not hard, just a pain in the neck from my point of view.  Where I run, we use Aristo, Bachmann, USA, Kadee, and Accucraft knuckle couplers with no problems. 

I would say find the company you like.  If you buy mainly Bachmann cars/locos, then stay with Bachmann couplers.  If you use mainly USA cars/locos, then stay with USA couplers.  Etc....  That is just my point of view on it.

Don't know much about it, but I do know that there are no parts available.

I doubt you will find parts from Bachmann.  The best place for parts (unfortunatly) is ebay.

Do you have metal or plastic running gear?  Do you have metal or plastic drivers?  That will narrow it down somewhat.

1) Not going to happen as they don't have spare parts.
2) I am assuming that it is the dealer selling you the card, which might happen, but I doupt.  If it is Bachmann, then it won't happen as they don't have spare parts.
3) Is the most likly to happen.

If you have the receipt, then go back to the dealer and tell them you want the correct locomotive.

I wish someone (Bachmann  ) would make White Pass #81.  It is Ex-US Army and I love the old US Military locomotives.  But, that's just me 

1) Not sure, but I don't think so.  Unless you look on E-bay

2) Yes.  All G-Scale companies will work together.

3) Yes.  It should be able to.

As Miller mentioned, the HO Thomas will not work with your North Star Express set.  I mentioned the HO-Scale Thomas was that if you could not find a G-Scale one and had to have some Thomas set, then you could go in that direction.  I should have been a little more clearer, my mistake .

Lionel was the only G-Scale company to produce a Thomas engine.  They have stopped making them for a few years now.  The only place you can find them now is on e-bay.  Bachmann HO Scale makes lots of Thomas engines and cars.

I run on Aluminum Llagas Creek track, and it is great track.  We run only Battery RCS so I would not know about electrical, but I would say it would be fine.