Here's what I use for my QT:
- Small powerhead for water movement. Just make sure you're not making the poor fish swim for his life against tsunami-like currents.
- Aquaclear Power Filter. I use the ceramic biomedia and carbon. It will take the biomedia some time to get a good culture of bacteria, so I'd suggest dropping it in your main tank (or sump) for at least a week or two before you use your QT.
- 3-4" PVC fittings to serve as places for the fish to hide. The poor guys are going to feel all exposed in a bare tank.
- A small heater is a good idea if you think it may get cold in the house.
- You're correct on no substrate. I usually just use ambient room lighting, but I've also been known to clip a shop light onto the side of the tank. It's more for me to observe the fish than anything else. In general, I prefer not to light the tank for more than 5-6 hours a day. I think it helps reduce stress, and the less active the fish is, the less waste he produces, and since many new fish are slow to eat, it will also reduce the calories they burn.
If your tank is done cycling, you can use water from your tank, but I'd suggest using new saltwater for the initial setup and then you can use your tank water for water changes. Speaking of water changes, I'd suggest doing frequent water changes on the QT. I'll usually do a 10% water change every couple of days. Pristine water conditions are going to go a long way to keeping a healthy fish.
Lastly, I'd be prepared for the fish to get sick while in QT. Most parasitical maladies can be cured with a freshwater dip, so you don't need anything special for that. I'd also keep some antibiotics on hand, both the gram positive and gram negative varieties (Maracyn & Maracyn-Two are good choices). If you get a clown fish, I'd also recommend having some Formalyn ready. It's a treatment for Brooklynella (a.k.a. clown fish disease). It's usually very difficult to find locally, and if your fish does come down with Brook, you usually don't have much time to treat it.