Congrats. And have a look at the movie Southern Comfort for a scary look at transguys trying to get health care in the states. It's a good idea to make sure you have regular physicians who are comfortable with you being trans before anything happens.
Sounds like endo #1 was pulling what he thought would be an easy opt out. Jerk.
And as far as the question, I used the name on my medical plan, then when I changed it, I told them. I was kinda pissed that they kept leaving messages for <oldname> long after I'd told them, and they were supposed to be a trans-friendly place. When I found out they'd been cutting my GP out of my test results, I asked her if she'd be comfortable prescribing T for me and, when she said yes, cut the endo out of my care.
Dennis