I changed my name legally about 6 weeks ago and now pretty much everybody uses my new name (with occasional slip-ups when they forget). But prior to that I'd already been using it among friends for nearly 2 years, and I have friends who've never known my birth name, so it wasn't as jarring as I expected.
I like AJ. I have a friend who goes by that name, but you should also consider male names for which A and J can be initials, so you have something to put down when you change your name legally.
Blood tests I hate. I apparently have veins that move and hide whenever a needle is around, so it's common for the nurse to have to stick me more than once to find one.