I meant to respond to this thread last night, but every time I wrote something I deleted it for various reasons and finally gave up. But I'll just try to quickly reiterate some things already said in this thread.
A. Support in the waiting room is a huge help. I was scared to death of the appointment and a lady I met on these very forums came to sit with me (on her lunch hour!), and that was the first time we had met in person. Her being there made it feel...less dire?
B. If you're prone to certain types of mental illness and/or you tend to be sensitive to the effects of drugs and stuff, then you'll need to be careful ~1 month in. The thing archlord was saying is no joke, I really wish someone had told me (or if they did that I had listened) regarding a large emotional swing. Hers was triggered from a different thing than mine (mine was stuff in my life going wrong at the same time), but there is, or can be, a pretty huge emotional shift at about 1 month after beginning or increasing dose. I'm pretty sure you've posted in some of my darker threads from those times

I didn't really pay much attention to my emotional state. I figured there would be a little change, especially over a long time period, but that the whole "women are emotional creatures" thing was mostly a stereotype. That's what I thought, right up to the point I was sitting in my therapist's office choking back tears telling her I felt like I couldn't do this and wanted to die. And then a month after THAT the euphoria kicked in pretty hard. Rinse/repeat for dosage increase.
Don't worry though, you'll be fine, I promise! Just get someone close to keep an eye on you, and try to keep an objective measure of your mental state if you think you may be prone to that type of thing.
As far as your "I'm for it/I'm against it" thing, I went through that too. Especially in the mornings, prior to HRT. I just felt SO masculine that it really threw me for a loop, and then by that evening I was like "Nope! I'm trans." That's all gone away. Now there's no doubt that transition is the way to happiness for me, though there are some other fears and doubts. Afraid those will be there until transition is over, but things feel more "right" every day.