the layout is going to be modular and the mods are 1 foot wide and 3 feet long to 1 foot wide and 2 foot long. one of the mods is going to be a train yard and more.
Where is your setting? I am modeling Great Northern and Montana Rail Link around Helena, MT.
not sure yet? northern mn . my grandma aldrich worked on a loging railroad in northern mn. she cooked for the crew that came in after the loging in the area was done and pulled up the rail and ties.
OK, I have a recommendation for you.
Make your MRR in modules as you say, but make each one a MRR switching layout by itself. That is; each module should have it’s own control panel and be wired so each one can be operated by itself as a switching layout. (The main power wires can be connected from one module to the next.)
Make your 1x3 module the yard and loco facilities if they will fit. Otherwise make the yard on one and loco facilities on another. Make your other modules towns or large industries. Each town should have a couple of industries plus a station and freight house. If you get one or more of them completed, pack it up and store it, then start a new module.
If and when you get a larger space, you can set up your modules, but space them out so you have more mainline run and scenery between the modules. (Add simple modules to fill in with just basic simple scenery.)
You don’t have to have any place or setting in mind when you build your modules. Just do what you want to do scenery wise. When doing scenery, some people pick an area of the country. To me, there are three different areas. Areas with a lot of vegetation, or areas without, and the desert. So just pick something that you like to do and go for it.