I've dated a few trans women and most didn't want to really have much going on down there. One girl would only want me to use my hands while playing with her tits etc, and another didn't want me down there at all. It was their decision and I respected it, even though personally I didn't mind.

I think that birth control is still safer, although after a long time on hormones they are like 99% sterile unless they are off meds for a while.

Realistically, it's something that you will have to bring up if it might bother you, and eventually you'll want to have a talk about when/if they are getting surgery, if you're comfortable with it etc. That's one thing about relationships, is that sex is important too. You will want to enjoy yourself too, but you can always trial run the sex and see what works for both of you. The one girl I dated only ever wanted to eat me out and that was fine too. She was good at it, and obviously wanted to make me feel good, and that was hot enough on it's own.