I don't think there is an "ideal" QT setup, since many setups will do the job equally well. However, I'm happy to outline my setup, lest you find that helpful:
1) 20g tank with lid and lights (day and night). A 20g works for me since the fish I buy are in the 1-3 inch size range.
2) Marineland bio-wheel filter. Many other filters would do the job equally well. I use this one, because I'm familiar with it from my FW days. It has a carbon filter and a bio-wheel. If I ever have to remove the carbon (for medicating), I still have the bio-wheel to support beneficial bacteria, plus I can put in regular floss where the carbon floss normally goes.
3) A heater and a thermometer.
4) An air stone and air pump.
5) Something for the fish to hide in. Most people use PVC pipe. I use various fake (inert) aquarium decorations that I had left over from my FW tanks (cleaned, of course). I doubt the fish care, but I like the look of them better than PVC pipe.
6) Seachem ammonia alert badge.
7) Dedicated supplies (not used in my DT), including a vacuum and hose, several buckets, a sponge to clean the glass, and a net.
8) Medications, including PraziPro (which I'm now using as a preventative treatment) and Cupramine (which I have not yet needed to use).
Also, I cycled my QT prior to its first use and I keep it up and running at all times. That said, I'm currently stocking my DT, so my QT pretty well always has fish in it.