Hey Heather,
We're about the same age. I've wanted to be a girl for a long time, but only discovered that it could happen a few years back with the wonders of HRT. So two years ago I made the decision to change my gender. I did a lot of reading online and research; and following the trailblazing of others, i've broken it down into logical steps:
1. Practice your female voice. (started sept 2005)
2. Start your facial hair removal. (started oct 2006)
3. Living part time female (started 7-21-07)
4. Therapy (started 7-28-07)
It's only just a month ago that I started to see a therapist. I think that before you even think of HRT, you should do those two things first (i.e. steps 1 and 2)--just because if you change your mind, they aren't life altering. In fact, probably not having to shave again is a good thing, male or female. So in the year it takes to get a decent female voice and to get some eradication of facial hair, you can do a lot of soul-searching on whether this is the path to take.
A therapist is good anytime. I only started late because I'm now ready for HRT and want to get it medically monitored instead of self-dosing.
oh yes, getting finances in order is a biggie to. If i do happen to lose my job when i transition, i have a decent nest egg to carry me through until i can land another job.
So, in the year or two it takes to clean the face, and get the voice down, save money!
Finally, for me, I've been able to work on my voice even more because I now live 3 days out of the week as female, and going out and meeting people has helped immeasurably with my voice work. No matter how passable my voice is on the recorder or even over the phone, talking to people face to face is much more demanding.
oh yes, i'm pre-HRT. so you can do a lot before you dabble in physical changes.