For your first session, don't expect much more than just getting to know each other a bit, talking a bit about your goals and where you're at. See if you vibe with them. It's one of those interpersonal things that you can't really objectively measure. Relax, feel them out as a person. As to self diagnosis: i think with a new therapist there's a bunch of fundamentals before you get to those more significant issues. Once you do, be honest and open. Tell them you suspect you may have something like it and why you think that way and they should take it from there. But honestly, don't expect too much from a first chat.