I fully agree, if you can quarantine something, you should.
As for the mandarin, I don't recommend hypo'ing it. They're fairly resilient to ich due to their slime coat. I have quarantined mine in the past. I took rocks from the DT and refugium and also seeded the QT with pods before purchasing the mandarin. (side note, this really should only be done in a QT that has not seen copper or medicinal treatments) I purchased a very small mandarin both times. For one, I had to re-seed just to be safe, but for the other, the quarantine tank actually served as a place to also train it to eat frozen, so it can be really beneficial to QT them. You really just need to observe the fish and be aware of the pod population, but it's completely doable if you prepare ahead of time.