Straight man here. I was asked out by a trans woman and we started going out. Somewhat different situation than your question, as I never had particular fantasies of or attraction to trans women. We eventually slept together. I was super nervous, since she was my first date, first kiss, first everything. In the end we got married and are living happily ever after, so I would say it worked out pretty great.

Based on your question I presume you are particularly interested in the aspect of being with a woman with a penis. For me it was alright. It is not my preferred genital configuration for a sexual partner, so I was quite happy when she got SRS several years later.

Like Jersusalemspiderman mentioned, many trans women have a contentious relationship with that part of their anatomy. I am not sure what percentage of trans women are interested in performing penetrative anal sex on a man, but I believe it is fairly low; if that particular act is important to you, you may be going against long odds. It was not something that I desired. While my then-girlfriend was pre-op, we did anal sex with me as the penetrator. I occasionally performed oral sex, though she liked to give more than receive. And the handjobs were mutual. I also topped in a variety of BDSM activities, though that is not really trans-related.

Be aware that estrogen can reduce penis size. It can vary a lot person-to-person, though. My other trans girlfriend actually had a penis larger than mine.

Treat the trans people in your life with kindness. Society is often cruel to them.