First two layouts were single mains. They worked nicely, but I'm not an ops guy. I like main line running, some switching for variety, some maintenance in bays (in transition era, that means a turntable and roundhouse, a large machine shop, etc).
Second two layouts, including what I'm running now, are doubled mains. Very nice...if you have the room....AND...AND...the curves you would really love to have, or close, will fit, both inside and outside mains. Ask Sheldon how much he insists on wide curves, and why. Once you knuckle under and build 'em, there's nothing like 'em.
With that aside, you'll need at least one crossover set/double crossover. Two would be better, and get them as close to your yard throat(s) as you can, say within about four feet.
I don't really agree, based on my own limited experience, that a double main necessarily impacts on scenery space, although it certainly would if the room and benchwork are necessarily small. My space is much like yours, but I go around the room with a duck-under entrance. I have to stand in the middle and pivot as the trains circle around me...which is precisely what I prefer because the backdrop is always outboard and I needn't move along with the trains to appreciate the backdrop. I just pivot.
Once again, twinned mains are really neat for passing trains, even with trackage rights between two roads, or a pax train gaining on a coal drag and roaring past going in the same direction. Or passing going the opposite direction...it all works and is a lot of fun. And they needn't take up scads of room, especially on 2.5" centers. Most benches will be near 24" deep anyway...some a lot more.
Don't forget the crossover!
