Very nice plan and your train building plan looks really nice too! Everytime I follow these threads I want to start over on my setup. Yours has gotten better with each little change. I think expanding the building to accommodate some of the layout details was definitely the way to go, rather than trying to shoehorn the layout into the smaller space to accommodate the building size.
I ended up with about 40-1/2" to 41" or so for my layout height (depending on basement floor slope). It has 40" legs with 1/2" plywood for a top (I'm 5'-9"). That seems to be a pretty good height for the top so I think you would be happy with the 42". I would very likely go with 42" legs if I had it to do over. I have a few shop stools that I sit on and can still see everything on top (only one level), but no chairs.
