[EricH]

No such thing as asking too much. There is such a thing as asking too fast, but not too much.

CIM motors: Each gearbox takes 2 (or one, if that's your design).

KOP drivebase vs. custom: As you're rookies, KOP is the way to go. You can bolt, rivet, or (shocker) weld it. Tip: Make sure that you're 1" undersize in all directions. It's no fun getting to your first event to find that you don't fit in the sizing box.

6WD drop-center works well and resists turning a bit better than omnis on the corners. I believe the KOP chassis has a dropped hole somewhere on the side rails--that's about right. Yes, you will need to buy more sprockets/wheels.

As it's your rookie year, you'll want a solid drivetrain. KOP plus an extra set of wheels, chained with #35, is very tough unless you throw a chain--and there are ways to mitigate the damage even then.

You're doing some things right already: You're asking for advice, and you're organizing, and you're CADding. And working on the drivetrain first.