well, really, you want to be looking at amps. the motor will try to draw as much as it needs regardless of the batteries ability. so yes, it would cook the battery if its too high. the prop used has an effect on this, the bigger the prop, the more amps.
By Cheap pack, I assume you mean one that doesnt have a super high discharge rate.... lets assume it can handle 8c (pretty common) that means youre looking at about 32A per battery, or 64A combined in parallel. Just as a guess, Im gonna say you will need both batteries.
Watts is an expression of the amount of energy used by your motor setup. I believe the general rule is that you need to produce 50W per pound to achieve a rolling takeoff.... 75W/lb for decent aerobatics... and 100W+/lb for 3D.

hope that helps...