>>9515894And to finish off the train autism, here's some good looking guides I found from a quick youtube search
https://www.youtube.com/watch?v=Vb6xd5n_GaUhttps://www.youtube.com/watch?v=_SFWqj3O4lAThe first video is just a general train build to see some various techniques/details, while the second video shows how to build a basic motorized chassis for an 0-6-0 loco (With room to add leading trailing trucks). I'd recommend checking out BritishBrick's channel in general if you're looking to get into train MOCing since he has a few tutorials and WIP/Idea videos alongside videos of his MOCs.
If you don't mind paying for instructions too I'd also check out Block Junction, they've got a couple of different steam loco types (Mostly 0-6-0s but also a 2-6-0 and a 4-6-0) that you might be interested in looking at. They only do UK stuff but you could probably still take some notes on how the internals are done.