Here's a track plan I threw together in RailModeller. I think all the connections are within tolerance and I've found Fastrack to be somewhat flexible as well. Pretty basic with crossovers between loops and one long passing siding. Definitely room to add sidings, etc or reconfigure.
8'x18' is a pretty big space and you definitely have room for a more interesting track plan with space for grades to/from multiple levels, multiple loops, etc. Especially if you're willing to use a tighter radius curve on a couple lines.
