quarantine tank and meds?

For my quarantine tank I don't use meds unless I see a reason.

Same here, I have always used a QT tank for observation and acclimation. I only medicate when I need to except for Pleco's which I may treat for internal parisites right away just in case.

Same here. However, if I were to medicate in anticipation of something, it would really only be internal parasites. In which case, I'd feed something like Pepso food/garlic but not immediately treat the water.

It depends entirely on the type of fish in quarantine.
For most- no I would not medicate unless I saw a problem that called for it.

But I have Fancy Goldfish that are notoriously difficult to keep healthy as most come in with flukes and internal parasites. On them I dose praziquantel twice while in quarantine to ensure they don't bring anything into my system. Still have a heck of a time keeping them healthy, but with a clean gut and gills they have a much better start.