Well if you want to make another power supply on the cheap
http://www.rc-monster.com/forum/showthread.php?t=27554 that will powere like 5 chargers full blast (I've ran 3 chargers at once). I'll be honest I tried using a normal PC power supply, and even though the 12v side was rated like 13A's on the one I used after the charge rate was set to 4 amps it blew out. You won't have that issue though with that size of batteries as they generally get charged at 2 amps or under.
As for upgrades hmm if the ESC is brushless already (I'm guessing it is) make sure you set the ESC for lipo mode, andsee if you can set the LVC. Personally I set my LVC's usually to 3.2-3.4 volts per cell to give leeway. The Lipo alarms will usually kick in when a cell his 3.4 volts, and make a loud sound.
As for gearing you should get a cheap temp gun (duratrax has one for like $23) and monitor your temps if it doesn't exceed 150 degree's I'd not worry you only have to worry once it hits 180ish as that is when they usually fly apart. Gearing all depends on where you run it. Like for me if I run a RC on the street, or dirt the motor might run cool, but once it hits the grass might overheat due to the extra force it needs to push the RC.