46/13 should give you pretty decent track speed, unless it's a really big open style track. I don't think you'd want it much faster while your just getting used to racing.
46/14 should be as fast as you need it to go on the track, even once you get used to it, but if you do need to show off at racing, a 15t pinion would do that.
Geared 46/13 I don't think you should have any problems with temps, unless it's really hot weather or you drive really hard.
30 minutes racing will be close to the batteries runtime I think. You might get a few mins more or maybe few mins less, just depends on all the normal amp draw stuff. Plus if you spend a lot of time on your lid, that's time that your not drawing much power
