Plumbing two tanks into the same sump

Currently, I'm planning on hooking up five 60 gals to one or two large sums or refugiums in this coming week. I'm a bit worried about the sump overflowing etc. but I have a wet/dry vac handy.
Would it be wise to use multiple (3) return pumps, 500GPH each or just use one large return?

 

I think your return pump is more than adequate so be sure to put gates (I don't like balls for slowly restricting flow but that's up to you). I have a 75 display and 33 frag tank and I run an Eheim 1262 on it which is something like 900gph @ 0' head.

I would never use a siphon overflow box, personally, too much hassle/risk. If you're still setting up the 20g why not drill it?

My system is a little bit different because I run herbie drains on both my tanks, that's where most of my intricacies come from. If I do another system like this in the future I may go with 2 return pumps in one sump. The herbies are a little trickier than a regular durso or other standpipe though.

One thing I did that was maybe overkill, but I put a gate and ball valve on both lines of the return so I could isolate each tank if I needed to. In case you have a spill or something go wrong in one tank you can flip the ball valve and shut off the flow easily to one tank, you just have to be sure your drain in the other one can handle the flow from the whole return pump or you have to dial it back with the gate valve before flipping the ball valve.

Also you will evaporate more, a good bit more than you do now, more surface area = more evaporation so make sure your return chamber in your sump is large enough to accomodate this or make sure you have a trustworthy auto topoff.

That's all I can think of off the top of my head, it may not apply but maybe it'll spark some other thoughts or something, good luck.