Greetings,
3 fans should be able to draw a good amount of air into the case. Heat dissipation will depend on your components. CPU cooling, number of GPU's, etc. You want to maximize static pressure and air movement front > rear or up and out, depending on the set up. Generally speaking, the things that will effect cooling efficiency are ambient air temps, case placement and whats inside.
Without knowing more about your components, its only possible to give general recommendations. I usually err on the side of more fans when possible. Good quality fans spin slowly and still move considerable volumes of air. Ensure you are using 4 pin fans with speed control. I like a quiet system.