voltage

First off let me start out with i have a Trex 450 Pro 3gx that has been upgraded with an phoenix ice 50 esc, scorpion 2221-8, & currently runs on 3s lipos. My question for that is how do i go about to figure out the max voltage i can run ie cells i can run on it at once either in parrellel or...

Can someone plz explain WHY the amp goes up when the voltage goes down? I really don't understand, because in RC on road cars, there is "classes" according to lipo cells being used. For example, 6s class, 8s class, open class, etc. So obviously the higher cell class pulls more power, and are...