[Sk8r]

...you keep the filter clean and test daily or twice daily.
An uncycled qt should be totally bare of everything but water and maybe a pvc elbow to let the fish feel there's cover. It's just saltwater. In fact, because you test them daily and possibly more often, they're safer than a cycled qt that's gotten a little toward the edge. You need a floss filter you can check daily for stain of any kind, and just keep that filter scrupulously clean and don't overfeed---what you're doing is making sure that tank DOESN"T cycle. You must not run carbon while using copper or antibiotics, but it's a good thing to run if just in for observation.

An uncycled qt can be an old salt bucket you can bring to spot on water conditions and hold there. An uncycled qt can be packed in the closet stuffed with spare laundry until needed, and set up with 10 minutes if you have water to use---use NEW water, not tank water---and it's as warm as the tank. It doesn't MATTER that it's not ro/di: you can use tap water and some from the hot water tap as a basis for the salt water to get a jump on the heating situation: just use water conditioner [I use Prime] to get rid of the chlorine ---but make sure the salt mixes thoroughly (use a strong mixing pump until that water is crystal clear)---unmixed salt can burn your fish's gills terribly.

An ATO on that tank is a Very Good Idea. That keeps the salinity spot-on 24/7: absolutely critical with meds to know that evaporation isn't concentrating them above safety, or that adding water isn't diluting them: you can lose a fish on that issue.

A jump shield is a must.
A heater is. A thermometer is.
A light is optional.
Dirt is the enemy in this set-up: no rock, no sand, no 'used sponge', and no stain on the floss---if it stains, toss it and install new clean floss, nothing remotely resembling it.