Russell, I think you will find building this as a modular layout will prove to be a lot of work. Lionel "O" gauge can be a lot simpler since track switches and many accessories can use track power. In "S" that is not the case. If you put in the 8 uncouplers I recommended but no additional accessories like a billboard whistle, switch tower, semaphore, or street lights there will be 57 conductors running from the control panel area out to items on the layout. When Lionel owners would look under one of my Gilbert layouts they were always surprised at how much wiring there was. I have built over 40 different Gilbert layouts for myself, all between 5'x8' and 6'x10', none were modular for basically this reason. It was at least for me too much work to build it, followed by extra work to disassemble then reassemble the layout modules.
Next step is to mock up the track to verify fit and operation, then start building. Have fun with it!
