Several things to think about:
1) Need much more info - how much space do you have available?
2) Do you have a specific area or location in mind? That will help. Right now you have some good goals, but they are pretty general.
I'll say this from my own hard experience - unless you are planning to construct modules from the start, forget about moving the layout with intact pieces of scenery and track work.
I started the PRR Panhandle with the delusion that if I made it lightweight, I could take it apart and move it (relatively intact). I made a number of butt-joint construction tables (2'x4', 3'x5', 2'x5', etc.) out of 1"x4"s. They are fine - very strong with sturdy 2"x2" braced legs. However, I used 3/8" plywood for the subroadbed (big mistake) - that required a lot more bracing. Plus when you go to a cookie-cutter subroadbed design (elevations and depressions), you'll need a Sawzall to dissassemble the layout. Wiring? That needs to be modular as well. By the time I got to wiring the layout, I had become much more realistic about the chances of actually moving it. If it ever comes to that, I will dissassemble the layout and retain the tables, wiring, track, and roadbed. All buildings will be removable and scenery will be foam-based.
So when it comes to portability - you either have to go truly modular or forget about it.
You might also want to get yourself track planning software - it's much easier to make mistakes on the plan than on the layout. Cheaper, too.
I would take advantage of this forum and keep throwing ideas out here. It can only help.
Best of luck,
George
