The brushless version is definately worth the extra money.

the brushed motor in the epx can handle a 2s lipo...the ESC on the other hand cannot.

For your project, the volcano should work. The upper deck of the chassis could be modded to hold a large plate in which to mount all your FPV gear.

If it were me, I would be tempted to lock the rear diff. while it is a 4wd truck, if 1 front and 1 rear tire were to be off the ground (or not get any traction) then all the power will go to those 2 wheels and the truck wont go anywhere. It wont be fun as a FPV truck if it gets stuck. But if you lock the rear diff then it will be really hard for it to ever get stuck.

Normally, I wouldnt suggest locking the diffs, as it limits tight turning and handling to a degree. But with your project, id say the gains would be worth the reduced handling.