[lincpimp]

1. The 8000kv is faster, assuming the same voltage is applied to both motors.
2. A 6cell rated esc is rated for 6 cells wired in series. So you could wire 2 3cell packs in series and get 6s, or you could wire 2 6 cell packs in parallel and have 6 cells worth of voltage and double the capacity (mah)
3. 2 motors should produce twice the speed, by allowing you to gear up, but you will run into other issues like diretrain drag and wind resistance that usually increase exponentially as speed increases, so NO.
4. Most sensorless systems produce more power than lrp and novak. You can use higher voltage on them than 2s lipo, so they will produce more power (simple explanation, a better one will most likely be given by someone who knows more than I)
5. Lipo batteries do not explode, however if they are improperly charged or discharged they undergo a chemical reaction that produces gasses that will make the pack expend (puff). I have puffed a few and yet to see any explode. They may pop due to the pressure, but no bomb-like explosion will happen. Sometimes they catch on fire, but I have not seen that happen either.

A link to the heli setup would be handy, although they will most likely not have reverse or proportional brakes, so you may want to stick to a car esc, like the mamba 25.