To get more action in that space, I definitely wouldn't go bigger than O36. I would stick with Plasticville structures too, which means "traditional size" (not scale) trains, unless it's a small switcher. Most traditional locos are pretty happy on the smaller radii. I would probably use Ross O31 or even Atlas O27 to build this.
At least 2 panels and maybe three. (A 4x4 panel with framing, wiring, track, etc., can be quite heavy for one person to handle, unless you're a pro wrestler or an NFL hopeful. Everyone drives SUVs these days, but if you don't, it might not load into your car!)
Good luck and please post some photos of what you built, how you joined the sections, and what the finished product looks like all set-up!! Thanks for sharing!
