Sump for 585gal.?

I am in talks with a guy who has a 585 gal glass tank He is going to sell me everything from the stand to the tank and filters(a sump) that go with it. Basically a turnkey 585. But he said that the sump thats on it is only 30 gal. with a drip trickle on it.

I have never dne a sump tank yet and I know enough that a 30 gal sump on a585 is way to small. So what size sump should a tank of this size have? I was thnking 100gal+ and do a DIY. But like I said I don't know anything about sumps yet.

I don't know if I can fit a 6' tank under this stand. The tank is an odd shape it's not a complete L it's kind of like a 60 degree angle. One side is like 6' and te other is 5 or 6' So without seeing te inside Of the cabinet yet. I am unsure if I can fit somthing that big under the stand yet.