If you are using cupramine you are fine to use it with prazipro. Relax a little and don't get in a hurry with quarantine... I usually don't mix the treatments unless there's a very good reason too. Keep an airstone in the tank somewhere... Dissolved oxygen is low when treating so it is wise to supplement.
It sounds like your fish is eating now, but I will throw this out there anyway. It has taken a full day or two to get almost every tang I own to discover the seaweed clip, sometimes longer. It isn't exactly how they graze in the ocean so keep that in mind when training them onto a clip. +1 on the selcon. I will soak mysis and the rest of my homemade blend in that and zoe every few days, especially if the fish needs to put weight on. Good luck with your tang!