Few questions, new 90 gallon setup


I just got a 90 gallon that I'm setting up, not sure if it will be fowlr or reef yet (based on lighting budget frankly) and I have a few questions.
First off how much volume of water should be moving through the sump? I am going to do an overflow box as the tank isnt drilled and its just easier? I want to be sure I get the right size overflow. I think I'll be using a 29 gallon aquarium as a sump and not sure what I'll be using as a refugium but it will be not part of the sump.
Also for fish I really want to go with tangs. I know they need room, which is why I went with a 90. I already have a baby foxface (one spot) and a baby two spot bristletooth tang (blue eyes awesome!) they are both about 3-4 inches. I also would like a sailfin tang, purple tang, and carribean blue tang. My local reef club is being tough telling me that those 5 fish alone are too much for a 90, but there is someone with a 75 on the club (and a board member no less) who has 4 tangs and 2 triggers. My biggest concern is what order to put them in, or should I put them in all at once? (I am getting them very tiny from a wholesaler who is MAC certified and they will never see LFS water, so direct to display is okay).
Also I'm looking to get advice on a skimmer, as I know for sure I'm going to be pushing the limits of the bioload (I'm doing this on other tanks with no ill effects except I run through 2x my tank's volume in water per month, lots of salt). My 56 gallon has in it right now 2 black percula, 1 maroon clown, pink/blue spot goby, 5 firefish, foxface, two spot tang, flame angel (cute bugger about the size of a quarter right now) and I still manage nitrates 0.5 :) I was thinking about an ASM G3, but if there is something else better in the 200-300 price range let me know what's working for you.


overflow will probably be 600 GPH or so, just make sure the return pump is smaller than the overflow after you account for the pumps head pressure loss.
You can't put a sailfin and a purple together let alone in a 90g. None of those tangs should be kept in a 4' tank.
If you want a tang that will be ok for a 4' tank I'd reccomend a yellow or a hippo.
My LFS recently thought they could get away with it and put a few tangs in a 90g in thier store for show. Well, what it showed was that they all died within a couple weeks.