Wow, Jeff, really great progress. I was worried about your grades too, but they seem to be working out.
A couple of people have commented on the difficulty of using O72 in a 9' x 13' space. 108" is of course plenty of width for 72" diameter track- the problem is if you want a complex track plan, multiple loops and engines to be able to run anywhere on the layout. Since, when you come down to it, most of us run a lot more than we switch, here is one possible solution.
Simply make the O72 a completely different layout on another level and unconnected to the other level ( either above or below) and run the big trains on that. On the second level, use a smaller radius and a more complex track plan and do most or all of your switching on that level.
