Nate...what is the vinegar for?
I have a 15 gallon qt with an emperor 400 hang on filter, no substrate and a few shells in there for the fish to hide amongst...a heater, and that's it. If you set up a qt and throw in a couple bags of biospira marine (live bacteria made by marineland which the lfs may have in their fridge) you may avoid your qt cycling....I used the freshwater one in my chinese goldfish bowl and it never cycled. I figure its around 25-30 gallons. So I think this is your best bet...otherwise you can buy the ready made seawater sold in some lfs which already has bacteria in it. and try doing water changes always with that to avoid the qt cycling. but no guarantee, it may still cycle nonetheless.