Setting up QT / hospital tank is always a good idea, but remember that this is a designated QT and/or hospital tank, not another setup. Therefore, if you are planning on using the "QT" as a hospital tank, then don't put inverts [including live rock] in the tank. These setups should be thought of as a "holding" tank, not another display tank. If you put inverts/live rock, then you cannot medicate the tank [which kinda defeats the purpose of a hospital tank]. Also, some hobbyists use QT to medicate newly acquired specimens. Meaning, that even without visible signs of parasites, or even bacterial infections, the hobbyist will put a new fish in a medicated tank during the quarantine phase to ensure that it does not have ick, etc, or get it before it goes into the display.
Also, as for substrate, I would suggest keeping it simple, meaning no substrate, and definately no UGF [mind you I use UGF so I'm not anti UGF]. The reason no UGF is because your UGF relies upon optimum tank conditions and biological conditions to run appropriately [which you won't always get in a medicated hospital tank]. Its a lot simplier to clean up a barebottom hospital tank than it is one with a UGF. Also, remember not to use carbon to run in a medicated system and NO live rock.
As for "seeding", yes do this to get a new QT going, but only if your seeding source is good ----like from your healthy main display. Don't seed from a tank where you are having problems with ick, etc., otherwise you will also get these problems in the QT.