Drilling holes for huge FOWLR??

[SeaHorse_Fanatic]

I'm helping someone set up a 300g Fowlr, with a 180g below tank sump & perhaps a 225g secondary sump/reservoir in the garage. The main display will be 8' by 2' by 30" tall. In designing the system, should I go with internal or external overflows, as well as what size & number of holes for those overflows & return pipes? He would like to end up with a well stocked FOWLR with perhaps a few hardy corals.

Thanks,

Anthony