I followed Ethan's blog for years before I was ready to transition, and he has a trans parenting blog that was active up until a few years ago. I haven't read through it, as it isn't something I'm considering yet, but there may be something there that resonates with you:
https://daddyhoodtranscribed.wordpress.com/My partner really wants kids in the future and has been giving it some thought. She figures as soon as they have a rough idea of where babies come from, we can drop the "Max is your dad but not your father" bomb. I view being trans as having a birth defect that I'm correcting with hormones and surgery. That is how I would explain it to my kids when I felt they could understand it. I honestly don't think there will be any issues with it.
The only struggle I have with it isn't knowing that the kids won't biologically be mine, it's that they can't biologically be mine in the way I would like. And unfortunately, I doubt the medical technology will get there in my lifetime.