It really depends on alot of things what is the minimum amount of fans that you need to cool your PC.
I recomend ducting more than anything else because it is so effective. I should really make a ducting guid so i dont have to explain this every time, but there is a cheap, fast way to do this, and you most likely wont have to run out and get things. all you need is a cardboard box, poster board, a ruler (to measure the stuff) and DUCTAPE lots of it!
so first, cut the cardboard box so you have a cardboard sidepanel, then, determine where the cpu fan is in relation to the side panel. then you want to cut a hole in that cardboard the exactly lined up with your cpu HSF. Make sure it is the same size though. then, measure the length from the side panel to the back of your CPU fan. Not the whole heat sink, but just to the end of the fan where it meets the heatsink.(Lets call the length from their to you side panel "Y") then maesure each side of your fan and add it up(lets call the added up number "X"), then, you want to make your posterboard peice X long and Y wide.
then, fold it into a pipe, but a square one that fits tightly around the fan. duct tape the seam. then put it on your cpu fan, DO NOT LET IT COVER THE HEATSINK and it should fit nicely between that and your hole in the side. To keep it on, ductape it to your psu. you should also put a fan on the end drawing in cool air. Make sure it is ductaped securly. then duct tape your side panel on and you have a duct that lowers temps.
If you have any questions, PM me