Welcome!
lots of questions...lets see...
-the gear set is good for customizing or acceleration/speed ratio (good for racing on tracks or drag racing)
-The colored tire set is made specifically for bit char-g and the tires in it are very soft. The tires in the black and grey set are made for bit racer-racer cars (like a bit but they dont turn...for special tracks). This set is much harder in comparison, and is valuable to have for race tuning. I would reccomend getting both if you are serious about making your car drive well.
-The tomy-made 2.6 and 3.0 motors seem to have a high failure rate (many people complain of them just running a couple of times and then completely burning out). I have heard that
www.bitchar-gmotors.com make their motors much better, and if you get a bad motor, you can send it back, and they will be happy to replace it.
dunno much about the NiMh batteries...longer run times, a little bit smaller..you can get them + lots of other stuff @
www.questformadness.com
hope all of this helps out...and if you have any more questions about the parts, look through the bit char-g guide on this page in the tips and mods section.
hope this helps out!
-nick-