Two Controllers one bot

We are thinking of using two controllers, one for the weapon and the other for the bot

We have a DX7 now, looking for a pistol grip second controller. We are the things to look out for, do you need two power sources?

You do not need two power sources. I know of no special instructions or warnings beyond the normal concerns for failsafing (and even then, it's the same as if they were in two different bots). We have done this with many bots, some with two separate circuits entirely (two batteries, two switches, etc), and some that share the battery but have separate switches and some that have the same battery and switch. It works really well, I think.

how do I do this?

Ya we did this a couple of times. All you have to do is simply plug the weapon ESC into the DX7's receiver, and the drive ESC's into the pistol grip's receiver. As long as both your weapon ESC and your drive ESC's have BEC's (battery eliminator circuits), the receivers will all power up once you turn the power on and should work without any issue.