What exactly are you planning to use? I bet their are builds you can see which use the same/similar workings. The primoo can easily handle daul loops so one loop should not be an issue.
Its quite an interesting build idea, especially for the primo case

to break it down:
1 x 420mm EK Coolstream radiator + 8 120mm Coolermaster Jetflo fans
1 x 360mm EK Coolstream radiator + 3 120mm Coolermaster Jetflo fans
2 x 240mm EK Coolstream radiators + 4 120mm Coolermaster Jetflo fans
1 x Alphacool Repack duel D5 res/bay
2 x Alphacool D5 vario pumps
19/33mm tubing (for maximum flow rate)
2 x R9 290X GPU's with EK full cover blocks
1 x i5 2500K (5.0Ghz) EK LTX block
....... And thats just the beginning, as for water cooling, however, all of this is still in the planning stages
The reason i have chosen 2 x 240mm radiators is due to how wide the Primo case is, so having one at the front of the case and then the second one being turned 90 degrees and facing the two intake fans on the side (i know there is enough room) however, not for all 8 fans, thats why they will only be push and no pull.