what are you trying to achieve? Meaning, are you looking for a precise amount of flow or are you looking at hitting a flow that looks like it works for your tank?
I think the best option is to start with a few holes and turn the system on, if it looks like its good enough, first time's a charm! If not, either increase the number of holes, or increase the diameter of the existing holes. Keep iteratively testing until you're happy.
Might also consider drilling some holes angled upwards to increase surface agitation.