You are correct in that the QT is not connected to the DT in any way; in fact, I keep my QTs in a completely different room so that it is MUCH more difficult to cross contaminate equipment when being careless. You have to make sure everything that goes in the tank gets a separate one for QT and DT... nets (if that is what you use), pipettes, anything that goes in the water does not go from one to the other. If you are using a tank transfer approach then the water quality is a little easier to maintain so long as you aren't going crazy with food every day. The fish only stays in the one tank for less than 72 hours and then gets all new water for the next almost 72 hrs. Once all of the transfers are complete you can then use water changes (which is how I like to do it) or the sponge which has been populated with beneficial bacteria like mentioned above.
The nice thing about keeping the QT setup is that you don't have to leave it up all the time and can get it pulled together quick due to nothing being cycled to have it fish ready. Heater, air supply, water motion, and clean water (which matches salinity and temp) is all you need to be ready for the fish. I suggest keeping the QT very simple. Before you get your first fish make sure you know EXACTLY how you plan to approach the QT- TTM, meds, only certain meds, etc. There is nothing worse than realizing your fish has ICH and then you are winging how you want to approach it.
