there is nothing wrong with using all fan slots however its likely not required.
at a minimum you want one front, one top and one rear. the top is even optional depending on your system specs and temps.
putting more fans in is NOT going to cause it to heat up. that is just silly. you dont want all intake fans... but you should have more airflow coming in than out. perhaps a 60/40 ratio (since air will find its own way out through cracks, holes, etc)