Greenbean,
It's fantastic that you're almost ready for this next step-it's a hard journey you're standing at the precipice of, but oftentimes it can be a very rewarding one!
Now down to business...I don't know what sort of climate you're living in, and considering that before coming out might be a good idea-is your family progressive? How did they react to the news that you were gay? What about your friends? It's important to consider this before you come out-some parents might be able to help you work through your gender issues. Others might respond well if you approach the issue from a more scientific and rational perspective, after you've figured it all out on your own. Some might not take the news well at all, but come around given some time. It's important to consider what sort of reaction you expect-sometimes, it might be best to wait.
It also seems like you're still figuring out exactly who you are-and that's a wonderful thing. However, it might be useful for you to do a little bit more soul-searching to really discover who you are before making it official. One thing that really helped me work through things before turning to my family was therapy-it's not always easy to find a therapist who has experience with trans* issues, but having someone to talk might help you deal with the struggle you're going through right now. Transitioning is a huge decision, and it's never a good idea to commit to a decision like this without seeing a professional, at least in my opinion-it helped me more than I can possibly say!
My last piece of advice? If you're worried that someone won't be accepting, be as calm and rational as possible. Oftentimes, parents will think that this is just some sort of phase (mine did), and write it off as that. If you are able to stay calm, collected, but remain forceful, they'll take you more seriously. I made the mistake of coming out to my mother too soon-I told her I was transgender, and when she asked what that meant, I froze up and started to cry...that's exactly what not to do! For someone as important as family and close friends (unless you're sure that you can share your struggle with them), it's best to make a definitive statement-not raise a question-"I am transgender"-not "I might be transgender".
Anyhow, that's my advice...I hope all goes well.
Best Wishes,
~Sasha~