I do not claim to be an expert on anything (exept maybe annoying my old lady), but I have always had good luck with my fish so im gonna put my two cents in. I do not qt my fish 1. because i dont have the space and 2. because of the increased stress.
The store I purchased all my fish from ran a low level of copper in all of the f/o systems. does that mean non of those fish carried ich? no. does that mean Ive never had an outbreak? no. I had a pair of wild caught true percs and no matter what i tried those fish constantly got ich. I went so far as to set up a medicated tank for them and watched them slowly wither away.
If you are not going to qt I would suggest the following: spend a few minutes looking at the particular fish you want to make sure its in good shape, ask the store owner if he/she is running any meds, ask if they use a uv sterilizer, ask how long theyve had that particular fish in stock, avoid wild caught fish when ever possible.
If you do have an outbreak there are some natural ways to deal with it, they are not always 100% effective but what is? Raising the temp a few degrees is helpful (i believe it speeds up the life cycle of the parasite, not sure though), adding a garlic supp. to frozen food is helpful, cleaner shrimp help out aswell.
I know alot of guys out there qt everything and that probably is best practice, but over the decade Ive been dealing with salt Ive found that if you're on top of maintenance (water changes etc.) and the fish is not ill in any other way a few ich spots here and there is nothing to go crazy over, and is certainly not worth breaking a tank down imo.
something like 99% of all fish bought in this hobby die within the first year of ownership. thats a horrible stat and im sure that the number is much lower for members of this forum. But everyone loses a fish here and there, I think that breaking down a tank for a few ich spots is probably going to do more harm than good. Im sure there is ich in my tank, but the fish all seem healthy and none of them have had any spots in the last year so i dont worry about it. So theres my advice, that and a buck will get you a cup of coffee!