[Mr V]

Instead of having to go out an buy a deep cycle automotive sized battery you can run two FRC batteries without running them in parallel. Use one to power the control system and a couple of your motors and another to power the other motors and the LEDs. You will need a second "main" breaker but you don't really need to have a second power distribution board. The FRC legal circuit breakers are of the "Maxi Fuse" size and you can get Maxi fuse holders, often sold be mobile audio suppliers. You would only need one digital side car to drive all of the motor controllers. The motor controllers have opto isolators in them for the signal input. This means that they do not have to share the ground system with the power supply to function, though you certainly could tie the grounds from the two batteries together w/o causing problems.