I took some time choosing a name, but did it in steps. Before I knew transgenders were real, I had people call me by a nickname that had nothing to do with my given name. Although it raised some eyebrows, no one ever said anything. From there, I had my name legally changed to a name that could go either way. Once I found out that transgenders were real and that I could transition, I again legally had my name changed from the androgynous form to the masculine form. I had an attorney do to make sure it was legal, and keep the copy in a lock box.
When you do decide, how you go about legalizing it will differ dependant on the state you are in. I was in upstate N.Y. at the time, and once a person was on HRT and had chest surgery, they could legally change their social security to be connected to a male. Same number, just changed the gender. I was adopted, and my parent's didn't think i had a birth certificate. They were only given the papers with my surname. Presently I am having my birth certificate legally changed to male. That involves, at least here, having a Dr. write a notorized letter that I have had the surgery needed, the counseling and how long I've been living as a male.
I would suggest doing everything through an attorney. Mine did all the court stuff for me, and I never had to set foot in a courtroom. That may be different in different states. Make sure to have your social changed and your birth certificate after the rest has been changed. If you do it legally, its just safer. I know attorneys can be a bit expensive, but its worth the peace of mind you will get. Good luck in your venture.
sam1234