Hi, I am by no means an expert on taichi, qigong, or bagua. But I do know a bit about them. First off, adrenaline can help you quite a bit but the thing is, like you say, it can cause negative effects. So learning to harness that might be a good way to go. I know next to nothing about that so you'll have to consult someone else.
But I'll try to help you a bit with the deep breathing. What I do when I'm in a stressful situation is say something that would either calm me down or rev me up and repeat it in my mind. As I'm saying this I breath deeply (ie from your stomach). Since your going to be in a fighting situation I suggest saying something that would rev you up a bit. I, myself, say 'no fear', and it helps. This will take a bit of practice but try to (as cliched as it sounds) empty your mind, breath deeply, and say that one phrase that revs you up. So when that fight comes up and youre facing your opponent do as you practiced, and if that adrenaline starts up, try thinking of that surge as your ki or energy running through you.
And as for some tips... try not to concentrate too hard on any one thing, even your breathing. Cant think of any else at the moment
If you need any more help feel free to message me. Good luck to you.