For railfanning I'd definitely go double track - the space you have is large enough that you could easily have two trains running "half a loop" away from one another resulting in plenty of traffic through the central town. I'm constructing a layout based on the PRR with a double track main with a maximum bench width of 20-21", and I'm finding that there is plenty of room for scenery, sidings, etc. - anything much deeper than that starts to have reach-in issues anyway.
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!
Double track mains are pretty impressive, especially when running heavy traffic. But, when you are pressed for space, crowding in that second main may take away so many other layout possibilities (i.e. industries, sidings, special scenery, etc.).
For what you are describing, perhaps a passing siding might be a good substitute, or maybe the space could be used for a secondary track - not in line with the original main.
No way am I knocking a double main, but they come at a cost.
In the end, you may want to just lay your track on the benchwork and fiddle around with alternatives. Software and scale drawings are really great tools, but nothing compares with just placing the track on the ol 4x8s........
ENJOY !
Mobilman44
Living in southeast Texas, formerly modeling the "postwar" Santa Fe and Illinois Central
I am presently tinkering around with a design (AnyRail) for a new layout and am not sure about reality vs what looks good on paper. Basically, am I trying to cram too much railroad into too little space? (Serious downsizing took place in this retirement move).
Space limitations have me pretty well restricted to a classic dogbone footprint with 4' x 8' islands, or bumps, at both ends and a 16' x 20" deep shelf along a wall connecting the two. I would like to double track the mainline which would converge at each end into a single track reverse loop for continuous running. In between I want to include a crossover and a couple of passing sidings.
Salvaged items from a previous layout consist of several industries, a 5 structure town, a passenger station, and a 2 bay engine repair shop. So I'm good to go with a start on scenery.
Meanwhile, any insight as to the practicallity of a double track mainline taking away from the available space for scenery and switching will be helpful. Thanks.