If you are debating, hypo, copper, meds, FW dips, etc., I would look at the specific piscine species, because reactions to certain methods differ greatly.
I have a hard time hitting a fish prophylactically with substances that may tax their system, or perhaps even harm them, but I do believe that with certain species and the prevalence of infection upon possession, that is just what you might have to do to give that species the best chance of survival. Tangs, particularly PBlueT and hippos, always seem to get Ich. Most folks I know around here (SoCal) treat them upon arrival, regardless of symptoms. I obtained a purple tang and didn't, and it had Ich within 48 hours and I was treating anyways.
I have done short FW dips for corals. But I seem to get better results with CoralRX, MediCoral or Lugol's, so I have no discontinued. FW dips for fish infected with Ich can work, but (from my experience), the benefits are only temporary...the Ich life cycle won't give up that easily. If it gets into an established tank, unless you can yank the fish, medicated food (garlic, metro, focus) has been the most successful for me. And if I can get them (and by them, I mean all of the fish, not just the infected ones), then QT with either copper or hypo has been my most successful (but never both!).
Please understand these are just my personal experiences/beliefs, so take them for what that is worth.
As for QT, I have a 20 and 40, glass, cleaned and sealed (saran wrap), ready to go a moment's notice. I use an aquaclear 20 or 40, heater, and have a few left over maxi-jets if needed. I use an old T12 fixture.