As someone who has gone through the induction into the sport recently, the best advice (as some others here have said) is to go to the track you plan to race at and see what they are running. This serves two benefits.
1. Your equipment is on par with the other racers, meaning you just need to focus on skill level.
2. If anything breaks, or misbehaves, you have experienced people on hand who can help!
Basically every track is different, so motor and gear setup differs from track to track. It may also differ based on your driving style ie an agressive style needs different setup to a smooth consistent style as agressive styles tend to favour high acceleration to recover from braking and missed corners, whereas smooth styles can hold higher top speed at the expense of acceleration as they wont be slowing to stop as often...just what ive found so far, im probably over-simplifying but for now, just chat to the guys racing where you want to race.
Stock: XRay T3 '12, F1: Tamiya F104v2, Buggy: Tamiya TRF201, SCT: AE SC10 4x4 FT, Radio: Airtronics MT-4