I get that! That's the right mindset in my opinion. I hate when people just quarantine fish and add copper constantly to every fish even off the bat. But that thought process makes sense, and yeah especially tangs, they're pretty ich prone. I had 2 clowns and the female got ich because she was pushing away my chromis. I wish I had acted sooner, but I did a freshwater dip on the male clown and the clown made a full recovery! The female sadly passed away, she kept stressing herself by being aggressive toward the chromis for some reason. But luckily my Yellow Watchman Goby, Chromis, and Scooter Blenny all didn't even get ich. So it isn't the end of the world getting ich, but definitely should not be taken lightly. You're definitely taking the right steps. Garlic is great. It helps prevent ich, and giving fish places to hide and good acclimation will help a lot too. There are also products that you can add which help protect the slime coat of fish when entering the aquarium, and I don't think that can hurt, they may help with ammonia too. Fritz ammonia remover/conditioner is good in my opinion and helped with ammonia in my tank. Hope all goes well for you and your fish

Also maybe think of getting a baby brine shrimp hatchery, then you can have live brine shrimp on hand so easily. BRS sells a good one, it's simple but it makes it super easy and you don't have to plug anything in. (So you can better maintain your dragonet).