Is your tank drilled??? I assume not or you would be in the market for sump stuff......
Depending on what you plan on putting in it, a sump is a great way to add "extra" filtration to your tank.... Personally, I would have some sort of redundant system on it. ( cannister, plus sump sort of thing)
I have seen some heavily stocked tanks work very well with this sort of thing going.
I know you can run to a sump without drilled holes, but I have not done it myself.
If I were running a sump with a 220 in marine, I probably would have about a 75 gal sump.... I'm sure others may have a better recipe for the size but my thing has always been "bigger is better" you cannot ever have a big enough sump, so the largest you can possibly put in there is the way to go..
good luck.....
I'm jealous...
david