I understand the concern this hobby can definitely be nerve racking at first. Personally I have never qt'd or did anything with inverts other than acclimate and I never had any pest problems. Corals I freshwater dip and inspect the hell out of. It's also good to get corals from a person rather than a store in my opinion because most stores do not dip or qt they move a lot of stock and don't feel the need to. Although I strongly disagree with this and think it's plain irresponsible on the vendor's part but that's a whole other debate that was already had a few months ago lol. Definitely try to check out the corals wherever they are before you buy them. Usually if they are in a member's tank if there was an issue with any infestation it would be noticeable.
@Awi definitely the best move as far as adding a heater if you have to do it in a bucket. Sometimes I will just get a huge bag or like even a plastic bag from a store or something depending on what it is. Even if you just place it in the sump and let it sit that works too doesn't necessarily have to float. Another lil trick