I don't know anything about surgery and how it affects having sex, but as for hormones, it's possible for your sexual preferences to change but it definitely isn't something that happens frequently, I believe. I've been taking hormones for over half a year now (though I'm on testosterone, not estrogen), and I'm pretty sure my orientation hasn't changed at all. I've heard of a few trans people whose orientation has changed during/after transition, but I don't know whether that is a result of hormones as opposed to having a new perspective because of transition, like you mentioned.

I saw your post last week about resources for transition - I'll PM you in a bit with a few links that might be helpful!