Hey, no idea where you are writing from as far as location and how safe you would feel doing so- but, is couples therapy with a therapist who specializes in gay/trans issues an option? It sounds like you are both rational and reasonable people but it might be helpful for you to talk it over with someone experienced in this sort of situation?
I don't know many parents, gay straight trans or not that ever regretted their kids, no matter how bad the other stuff in life, including the other parent got! I feel as long as both of you are committed to the kid I wouldn't argue against having a baby, but I think it would be wise to wait until you both have figured out the whole parenting thing for a year or so before starting hormones. Pregnancy and caring for an infant is a major life upheaval so maybe waiting until the kid is about 1 or so might help? It's a tough situation, but good communication and honesty will be your strength. I read a book where someone's mom freaked out because she thought waiting for surgery meant five years when it only meant a year! So I think having a timeline that both of you are clear on, with some wiggle room for "what if" scenarios would make you both feel much more secure...