[Chris is me]

I can't speak specifically for FTC (you can mathematically calculate drive load for your motors if you want, I could help with the math if you're looking for that much precision), but I can say a few things that should be helpful from what I've picked up:

1. Test everything. Build a chassis, put some weight on it, and figure out if there's a big difference between 2 and 4 motors. There's no substitute for figuring out how the platform in front of you works.

2. I can say you probably won't / shouldn't be draining a battery in 2 minutes. FIRST generally uses circuit breakers to make sure you can't draw that much current for that extended of a period of time. In any robot game, you shouldn't be anywhere near that number because 2.5 minutes with a perfect battery is 1 minute with a shot battery. Also, you would take a major performance hit at the end of the match.