re: chains. I recommend throwing away the kit chains straight away and using a KMC Z chain or other good quality common chain. If you have the money ($30-40) you can get a BMX half link chain (entirely made of half links) that will ride well and probably last longer due to even stretch.
Use a common ruler to measure chain stretch, or a Park chain checker. With a ruler, measure from center of one pin to the center of the pin closest to the 12" mark. If its over 12 1/8", or starts "shark tooth"ing the teeth, pitch it and get new cogs.
With these motor kits, it might even be able to stretch a little more and still make do.
