Well... I'm no guru and I don't have all answers... However there are certain concerns as per your questions...
1) I have not heard of ammonia spike for copper treatment... However, copper will leech onto rocks and you may not be ever able to keep corals unless the rocks are treated...
2) I do not know whether will re-freezing them will have any repercussions. But it's better to mix and feed straight.
3) It's not exactly a cure, but it does boost immunity against certain diseases like ich and marine velvet.
4) If you have no corals, invertebrates and anemones, it's possible to hypo DT.
Sorry for not being able to fully answer your queries... I'm still a noob...
Angel Keeper