Ah! with Gargraves and Ross you can do anything. In addition to the suggestions above (all good) I would think about keeping one side of your layout extremely narrow--just enough for the two-track main and enough scenery to keep trains from falling to the floor. This will give you an opportunity to have your workspace/modeling desk also along that wall.
If you do choose to stick with a single track main line (and your layout will look spacious if you do) think about a runaround track/passing siding in your yard.
If you find exchanging train consists a pain, then two or three double-ended storage sidings might be in order, either as part of your yard or (if you want to keep more than one especially long train on the layout) along one of the long sides of your layout.
You are wise not to try to cram too much into your space. If you're going to build benchwork with a conventional grid, remember that not all sections need to be rectangular. You will prize the open space you preserve in your train room as much as you will the layout itself.