Just Getting Back in the Hobby

[Sumpter250]

to Big Blue
From your list of "Givens", Modular would be the best way to go 48" X 20" (( 48" X 24" if you could stretch your reach just a bit )) modules, Perhaps a major rail line at one end, to pick up "inbound", and drop off "outbound" traffic.
The modules could have their own "legs", or, they could rest on an open bench-work, base.
I belong to a modular group, and my modules use a "simple open bench-work", that consists of four 6', " 2X4 I beams" ( 1" X 2" top and bottom, with a 4" vertical web made of 1/4" plywood, ), and four leg assemblies that the I beams bolt to.
It had to be portable.    
The "curtain" hides the bench-work, but you can see the bottoms of the leg assemblies, with the "Leveling adjustment bolts".
not all floors are level and even. The beauty of this "Bench-work/leg assembly" is that it can be moved to a new location, adjusted to "level", and the modules, just sit on top...........easily moved, and readjusted for the new environment. :mrgreen:
The module behind the center one has its own leg assemblies. These are 2" X 2" , 34" long, the bench-work legs are 30"long.
I used the bench-work, to reduce from eight, to six, leg assemblies....two less things to carry the I beams have "joiner plates' that bolt two each, of the four I beams, together at the webs, to make the 12' long base.
The modules are clamped together, where their ends meet.
This shot, taken at the last train show, clearly shows the I beams and their "joiner plates"
   
The "Three" have a trailer that they transport in, the center "back module" goes in the car.