I agree with your approach, and with @AFrame's post above. A few points to add...
1) Consider a basement with a bathroom or the ability to add one. Very convenient, especially when you have people visiting to run trains. If I could do only one thing differently, this would be it.
2) Consider the ease with which you can add electrical circuits.
3) An unfinished or minimally finished basement is a good starting point, especially since you feel comfortable doing the work. Not only does a finished basement mean that you're paying for it and will be demolishing perfectly good work, but it can hide problems.
