You can normally get away with 2 fans on a splitter connected to the MB with no or very little loss of speed and 3 fans will be ok too as long as they each never take more than 350ma. (most used to be 500ma)
The issue will be controlling fan speeds not the power draw, the only thing extra thing needing managing is the GPU heat and if you are doing that with a splitter - the question is whether you want to control that by referencing the CPU or case temps, neither is ideal but the CPU header is where you are most likely to see the changes faster but at the cost of spinning up all the fans when only the CPU needs cooling. - T
here are fan controllers with thermal inputs that will control the speeds of fans but the issue there is where to put and calibrate the thermal sensors to get the effect wanted. Easier to setup are
manually controlled fan controllers.
The machines themselves run cool and if your case has space for a fan directly above the GPU then a single fan blowing on the gpu will likely cool it down enough to not need more, otherwise normal fan placement dependent on case fittings and contents. (embedded links are to examples not recommendations).
And a heatsink for anything thats getting hot near the GPU (Northbridge is thereabouts? and will get extra work when the GPU is busy)