Good points!

By a whole map I mean a 2' x 3' space where I can have an encounter. You're right, an entire island wouldn't be workable...

My players have grown comfortable with me railroading them a bit since it means they get nifty terrain to fight on.

I play in my apartment, so I don't need to move things very far. The modularity for me will be more about wanting to be able to reuse pieces rather than having to make a new 2' x 3' space for every session... And yeah, I've been noticing that in model railroad terrain they get pretty heavy with the details, enough that you couldn't really put a miniature down in a lot of the spaces they make. I'll definitely have to go lighter than they do.