You admitted early that your yard is too small, good luck.
Big mainline engines on 4’ r. curves exist in smaller scales…
Start with an Aristocraft 0-4-0 w/ a tender and a small loop. Buy a closeout loco and see if your particulars can adjust to your physical limitation.
Worry about the other stuff if it matters, if you can’t adjust to the small curve limitations, the rest don’t matter.
Many use a following car for batteries, sound card and controller. I do. I’m in the Sonoran Desert and all trains have canteen cars with extra water. So room is no problem. I’ve seen canteen cars on some Canadian trains too. It’s a thought.
John