Generally a better way of doing a layout plan is to start with these two things:
1) Describe your vision for the model railroad - when you close your eyes and try to imagine what you would like to end up with.
Flatlands ? Mountains ? Tracks running down inner city backyards ?
Olden times ? 30 years ago ? Today ?
Passenger trains or freight trains ?
Do you want to be able to sit back and see the trains run past, or do you want to drop off and pick up freight cars from industries ?
And so on and so forth.
2) An overview of how much space you have available in the room where you want the model railroad (make a drawing of the room, showing stuff that you have to have free access to)
Then you can start worrying about how to accomplish your vision - how many plywood plates you need, how to cut them and join them and how to support them.
You say that "my workspace needs to be no bigger than two 4x8 sheets of plywood". What do you mean by that ?
That you are allowed to use 32 square feet of a bigger room ? How big ? What dimensions ?
Or that the room size actually is 8x8 feet ?
A 4x8 sheet of railroad takes up more space than 4x8 feet. You can reach max 30" (2 1/2 feet) in from the edge to fix a problem (like a car derailing). So you need access to at least three sides of the 4x8 layout.
If you are anything like normal sized, you should allow yourself a two foot aisle on at least three sides of the table - making it take up 8x10 feet. You can trim a _little_ off that by allowing yourself only 20" aisles instead of 24" aisles.
In general, you get more RR track length (and action) for your bucks by cutting big 4x8 plates into narrower strips - maybe a foot, 18" or two feet wide, and building "shelves" around the walls. By placing the shelves high enough that other stuff (cupboards, a TV set, books shelves etc) can go under the layout, you can construct a bigger layout without preventing the use of the room for other purposes.
A great book for planning purposes is John Armstrong's "Track Planning for Realistic Operations". A good book for building a support system ("benchwork") for your layout is Linn Westcott's "Model Railroad Benchwork".
Good luck with your planning!
Grin,
Stein