How much engines do you have?
I can confirm that 1 accumulator can cool at least 3 combustion engines. I use liquiducts but golden waterproof pipes should work as well. But I already had engines blowing up because stone pipes couldn't distribute the water fast enough.
@OP:
For the energy overflow you could use a redstone energy cell with a bc gate next to it, that switches the engines on when the cell is empty or off when it's full. How exactly you do this depends on how much energy you produce vs. how much energy gets used, and if it gets used constantly or not.
I have the following setup: The (simple) gate is set to "give redstone signal when no energy", this redstone signal goes into a pulse former, that activates a state cell, which then powers my engines for the designated amount of time.