I usually keep my QT tanks bare-bottom for ease of cleaning, but my brackish one has crushed coral since its more of a rehab tank than a strict quarantine, and I wanted the fish to be as stress-free as possible.
all you need is a heater, no substrate, something for the fish to hide in like some PVC pipe, a powerhead for circulation and a filter...as said above though, it will need cycling before you add fish to it.
You do not have to cycle a QT tank, as you will be doing a lot of WC on it. Most meds used for treatment will kill off any bacteria you had in there for cycling.
As niko said, it depends on what you're using the QT tank for. If I buy new fish and just need a place to hold them for 4 weeks before adding them, they go into a QT tank and get normal 1x weekly water changes, so I would want a cycled filter.