on pinion gears what will more teeth get me verses less teeth and are they all the same shaft size? thanks

Generally more teeth will give you more top end speed. Fewer teeth will give you more accel. I say generally because it is possible to over gear where adding more teeth will actually make you go slower. Yes, all RC pinions have the same size ID.

Bigger pinion drives the input shaft faster... I take very detailed notes, but simple notes might make it somewhat obvious what gear change is doing for you. Hank is very right. Sometimes you want to keep putting a bigger pinion on but very seldom does that actually make your lap time faster... But it will make parts of the car or truck smoke.