Calm down honey.
You're putting the cart waaaaaaayyyyyy before the horse.
It's good that you're trying to educate yourself. You should probably make an appointment with a gynecologist for a checkup and to talk about the things you have question about. She'll be the best person to advise you on contraceptive methods and which, if any, are right for you. See if you can find a Muslim doctor...chances are, she'll be able to better understand your concerns. Is there a trusted, married female relative or friend that you can speak to about your fears? Someone who isn't afraid of frank discussion? Talk to her as well.
As for labor, I won't try to sugar coat it for you. From everything I heard, it is very difficult and painful BUT, there are a number of things that can be done to help ease the process and make it a less painful one. I've also heard from many women that though it was the most difficult thing they've done, they'd happily do it all over again. And Allah SWT has made us women strong...he built us in such a way that our bodies endure the process and bounce right back from it.
But seriously, STOP worrying about this. One thing at a time like Sara said. You're engaged. Concentrate on getting to know the boy and his family better. Have fun and savor the present. There's a sweetness to this time that will never come 'round again. Once it's gone, it's gone. Once you're married, savor the time when it's just you and the hubby. The rest WILL fall into place, Inshallah.
Congrats on your engagement. :)