Unless you're QT'ing tiny fish like the Neon Goby, a 10G is too small. If you plan to keep normal fish, get a 40 Breeder for your QT. Hopefully you have a PetCo near you that sells them at the $1/gal price....if not use the closest tank to that size that you can. I wouldn't go smaller than 15 gallons....that's still
really small IMO.
Avoid the prison style QT's you see commonly where there's a heater, filter and PVC parts....beef it up with healthy, naturalistic background materials including some live rock and fake plants.
Don't think of QT as a magic bullet. It can be tempting, but plenty of folks QT "by the book" and go on to have tanks with sick fish. That's not what it's about. It's not a hospital tank either.
QT is an observation phase where you give them the most attention they're ever going to get from you. You get a chance to start getting your observational skill-set down pat and start getting your feeding routines in order. Figure out what live foods will work for you. Etc.
Yes, if the worst-case scenario strikes and you need to medicate, they're easy to catch and remove to a hospital tank...or if you don't have a separate tank for hospital
you can usually still medicate the QT with out completely killing it.
Unless you're getting your fish sight-unseen, it should be very unlikely that you need to medicate fish at home that you've pre-observed and hand-selected (e.g. at the LFS).