Thanks for all the great advice! So maybe instead of a 4 footer module a 5 foot one would be better but 2 feet is as big as I can really go. I really like this trackplan http://appalachianrailroadmodeling.com/tp_stonecoal.html . It will probably serve as a base for my design, and each module will either be a "scenery" or a "scene" module. The "scene" ones which will have coal mines or towns will be designed to be able to be switched for another module with basically the same track arrangement, but instead of a 50's era loadout one from the modern era would be there instead. Having that as a design feature would let me have a truly multi era layout since I could have it with all modern, 50's, or some of both for the 70's allowing all sorts of equipment to be able to be run. My main concern is getting the layout to be able to be able to be ran as an oval, staging may have to be the same as the layouts yard.
I actually drew up a plan when I was in high school with this concept in mind. What I did though was had a plan drawn up with 2 module "mate" sections that went together. The layout was a total of 8 modules and could be configured in several different ways. The only drawback was the 2 "mates" had to stay together to keep track arrangement and scenery to match. The reason I designed this concept was to allow for one to be able to take not only an entire layout to a show but to have sections instead. The other reason was each of these 2 module "mates" were their own specific theme, mainly switching. However, one of the module "mates" was a mountain pass.
