2) a. The higher the voltage the less range for a given battery size. If you run at 48v you could double your range for the same size battery. A smaller geared motor would be more efficient as well.
b. At 96v a 30amp controller will be putting out 2880 watts. So you will be getting close to the limit of a 3k motor. If your controller is bigger than that you could be spiking some serious heat into the motor.
96v is a lot of energy to be building and not know how to connect the wires. Would make a big spark if you did something wrong. If you ask at es they would be all over your questions. the 'bigger is better' forum. good luck