1. You can use the stock NiMH CP battery with the CP Pro, but because of the lower pinion gear and the symetrical blades you're going to get VERY poor performance. You'll be lucky to get it more than a few inches off the ground unless you pitch the blades extremely high, but then it will perform poorly with the LiPo, so I don't recommend it.

2. The difference between the 3 in 1 and the 4 in 1 is that the 4 in 1 has an integrated receiver, whereas the 3 in 1 is just the ESC, mixer, and gyro. The receiver is its own component on the CP Pro. The benefit is saving about $25 when the 3 in 1 burns up as opposed to buying the completely integrated 4 in 1 since receivers don't tend to get smoked very often.

3. The CP Pro is basically just a CP with all the upgrades. I fly a CP thats basically upgraded to a Pro (minus the 3 in 1) and it flies just as well as a CP Pro, however you cannot put a Tail lock gyro on the CP and they don't seem to react well to some of the other upgrades like direct drive tail.

4. The Autorotational gear is an add on upgrade for either heli.

Sorry, I don't have any info on the charger.

Chad