Something tells me that pump of yours is an overkill
Tubing would need to be 3/8" to each computer so each machine gets an adequet supply of water.
The bong itself would definately need to be rather large. You might even consider constructing a vortex cooler becuase of the large amount of heat youare trying to disappate.
Tap water COULD be used in the whole system but tends to leave too much junk behind in everything else. You COULD setup a dual cooling loop; one for the cooling tower that uses tap water, the other one for cooling the systems. There would need to be some sort of heat exchanger in that case. (Come to think of it, if you do decided to build that vortex cooling tower, that super pump of yours would come in mighty handy
)
That should be enough to chew on for now