Just breathe. It won't be bad, I promise. I was nervous as all hell when I went to my therapist for the first time. I was borderline in tears, because I had never been the type of person to talk about my emotions, and have never talked about them with a doctor. You'll just get some typical questions.. I mean every experience is likely different, but my therapist started out by just having me explain why I wanted to see her and what I was there for..
Then it was just all discussion. It wasn't like an interview. I didn't feel pressured. I just talked. About everything.
It is up to you to talk about your trauma history. I would at least say that I see a trauma specialist and they have made certain that your issues with your gender have nothing to do with what you've experienced in your past. It will allow your gender specialist a larger grasp on you, who you are, what you've been through, and what you'll be dealing with.
Also, you need to tell your doctor that prescribes your bipolar meds, yes. Because, in some instances certain mood stabilizers become ineffective with T injections, and with bipolar disorder, no matter how many meds you take, you still have episodes. It's just a fact. They need to be aware of you and your taking T because when you have episodes, they may be heightened from T injections.
You can get on T despite being bipolar. You just need to make it known.
But may I ask why you don't just see your regular psychiatrist? It doesn't matter if they are gender specialists; they can still recommend you for T..
But I mean if you'd rather go to a gender specialist, then that's all good for you - I just figured with your situation with being through what you have, and being bipolar you may be better suited speaking and trying to get approved by a therapist that knows you and your situation a lot more thoroughly.
I wish you all the best.