Hey Ryan,
You need to figure out which pump you want and how high it will be from the sump to the tank. Then you can figure out the appropriate sized hole (though I think a 1" bulkhead = 1 3/4" hole would be good for you).
I also don't think I'd feel comfortable with my holes closer than 3" apart...but I'm a paranoid kinda guy
Also, for turnover, you need to decide what type of corals and whatnot you plan to keep. If you are doing only SPS, they would need more flow than say, a tank full of LPS hammers and frogspawn.