Looking to convert an MBX5T

May I suggest going for a longer can Leopard? I owuld recommend that you go with the 4082/2Y/1500kv motor. Should give you a bit of extra torque I think. Price difference isn't huge neither. CLICK HERE.

Between the two ESCs you suggested I would side with the HW 150A XERUN because it has been around longer and has proven it self. I have a coule of Trackstars that I set up in friends cars but it is early days to comment on their reliability. Even with HW ESC remember that the MMM is only a few dollars more.

Yes you can remotely switch your servo off and all you need is a three channel radio and a switch like this one. CLICK HERE. Just power your brake servo from this switch so when you switch it off on your third channel your brake servo will have no power. Just make sure you get the wiring side of things right. Then you should be able to go in reverse.

You should be fine running Mobas. The wheel off-set will be determining factor if everything will fit and not rub on the suspension arm or the body of the truck. This you will have to figure out your self but you might need to go to wheels with half inch off-set is what I am expecting.

Make sure you post plenty of pics once you are on your way building this truggy.