every question is quite valid...
1. You'll never be cis, and your brain is very individual. You will always think as you think. Transition is merely an aid to make you feel more like you... if that makes sense. There is always sperm banking and seregate pregnancies later in life. I dont see it as 2 seperate lives, but merely as your personal life experience that has made you the person you are. I wouldn't be the woman I am today if it wasn't for my life experiences.
2. I can't speak for sexual reassignment surgery. I'd imagine that "if it feels good, it feels good" What's a few hundred nerve endings? If you enjoy the feeling of having sex, then what's the difference?
3. I stare at girls all the time. I happen to still be attracted to women... Sounds perfectly normal.
4. You have a good chance of getting wider set hips being younger. The magic of shoulders shrinking and chest measurements is that you lose muscle bulk to give you the appearance of a slimmer torso. I wouldn't worry too much about what an average woman looks like. I have cis friends with bigger shoulders than me... who are just as tall and that have had children and still have the same size hips as I do. We are all individuals... and come in many sizes.
5. There's no real way to know how far Hormone Therapy will take your appearance. Its very individual and genetically bias. Some people get more out of it physically than others. Being younger is a huge bonus for you, but its merely a guess. Medical science cannot predict our physical outcomes. As Dena said, it takes YEARS to see how things will turn out. There are a lot of Trans Women in the world... Not everyone of them choose to post and advertise. There are quite a few out there that you would never suspect as not being cis. Some Trans Women don't take transition as far as others... Its not necessarily an all inclusive picture of how well or how poorly hormone therapy works.
In the end, if transition makes you happy that's all that should really matter.