Welcome to Overclockers,
What cpu and gpu are you planning to cool? And why... silence or performance (overclocking) or both?
Case information would also be nice...
Water cooling just the cpu and gpu only needs 1 good pump like a D5 or Aquastream XT pump if you live in Europe. And a good 480 radiator or 2x 240 rads.
Dual pumps are used for high restrictions setups or for redundancy.