[asid61]

A cimplebox will not have nearly enough reduction, and will draw massive current from your motors.

At the very least, download JVN calculator. It will allow you to find good ratios for your designs even without knowing too much about motor selection (because that's what you use it for).
I don't know where to learn more in-depth stuff about motors though. The Vex motor curves are nice but do not tell you how to get those graphs, or how to interpret them.