Welcome mate, don't think you will fit an awful lot in a 2 x 4 so definitely go for the second board end to end if you can. Get your self a copy of Cyril Freezer's Track Plans for Small Spaces or whatever it's called and have a play with different ideas. Draw up a couple of plans and post them here and we can help with comments and suggestions. Perhaps his Minories plan would be a good start given the terminus aspect.