NOT A QT
! I thinks that's what you meant by "quart" right? It can't e used as a QT
tank as it shares the same water as your tank. You can't medicate in it nor use hypo salinity. Unless you know more about it, like the type of lighting and how effetive the skimmer is I wouldn't recommend it. A sump is supposed to be out of sight hiding your equipment and increasing water capacity. A fuge is to remove DOCs via macro growth exportation and provide an area free of predation for pods
and such to replenish your main display by putting fish in it you are adding predation. Yes it can be used as an isolation area in the even you need to separate some fish for some reason but I wouldn't make it thier home. But I guess you could if you really wanted to, but why not just get another tank for that?
So are you not skimming now? You may find with a lighter bio-load some hobbyist aren't skimming at all anymore with the addition of a large enough refugium they export enough DOCs with Macro algea growth and the use of mineral/miracle mud or nutrient rich gunk to replinish trace elements. I realize your setup is rather new and at the moment there probably isn't a lot of DOCs and skimming isn't necissary at the moment.
Do you have an overflow box right now, or do you need one of those too?