Having an effective, knowledgeable gender therapist who can listen and help you as you need clarity, discovery, letters, and more is good to have.
I would not be too concerned about what to say, if you cry, and how it will go. I do realize that these are all reasonable and normal concerns. Simply show up and be willing to answer questions. You do need to be able to state why you are there, what you need help with, desire for letters, HRT, and so on. If you have not made any decisions or timetables in that regard, say so if asked.
If your therapist is of little help, consider finding another before giving up gender therapy. Some may not be a good match for you, but you cannot determine that until and if you experience that.
Oh, when you go, dress comfortably, do not be concerned about “what you have to wear.” If you present as female now, go that way. If you do not, go with your usual look.
It takes a lot of courage to go. I hope that it goes very, very well for you. If you cry, that will be just fine. If you do not cry, that will be just fine.
I would be open with your answers. Let your therapist guide you.
You will be just fine.

Chrissy