I would say one 3x120mm RAD is enough for your system + 2 videocards. If you are going with 4 videocards, 2 RADs would be a good setup, feel free to make that 3, it it makes you feel more safe.
This is a very incorrect statement. Do you realize the total TDP at load these cards would produce in comparison with the maximum amount of heat-watts able to be dissipated by each 3x120 rad available, by model and fan speed?
At first glance, a 6970 has a TDP of close to 300watts...so a total of 1200 watts potentially at load....a RX360 can potentially dissipate ~550-575 watts with 3, 1800rpm fans (best case scenario). The OP is going to need at least 2 of these (or similar performing rads) and an additional radiator...this doesn't even take into consideration if he is looking to watercool the CPU as well...it would take at minimum three RX360 rads and maybe more...
Koolance doesn't really make pumps, they re-brand almost all of their pumps from Laing- which are also some of the very same models used by Swiftech and other vendors.