I have a 120mm Fan
on the side of my Antec One.
My 560ti runs at 99% 24/7 and doesnt go above 80C, my fan is connected to the PSU with a 'quiet' connector for low speed.
Just go with the front and side as intakes. You would prefer the bottom to exhaust not bring in dust but a fan exhausting will just pull the air from the front fan. If you can use a filter then it could be an intake, but I doubt you will need it.