Mike,
I think that you might need to back up a bit and fill in the blanks. I went through a phase where I collected all the 4x8 plans I could find, because I was convinced that I would build a 4x8 if I could just find the right plan...
From my experience, I would urge you to think about what industries interest you and your son. What era? What location? If a certain kind of rolling stock appeals to you... and so on. Do you like scenery - rural or urban? All kinds of questions...!
Once you do that, a bit of research will give you an idea of what your track plan should be. Certain industries, in certain places, at certain times operated in specific ways. You can start to string them together to give you your track plan.
For me, I ended up with 4 - 2x4 foot modules. Same square footage as a 4x8, but more what I wanted. My plan is a single main that enters a small Ontario town in the 1920s and 30s. There is a doubled-ended siding on the north side of the main with a team track, a stock pen, and a grain elevator. A facing siding on the south side serves a coal dealer, an ice company, and becomes the house track for the station. At the "end of the line" there is a turntable and a small engine servicing facility. I have plans to expand with a sawmill, and a "forest" module, but for now that's it.
It took a bit longer to figure it out (or did it, as there was no end in sight for my 4x8 searching...), but I am happy every time I think about it, and every time I work on something to add to one of the modules.
Hope that helps.
Andrew