Well, I'm not a labor/delivery nurse, I'm an ER nurse, but I'll go ahead and share my view on things!
OB was my favorite clinical...there are a lot of different things to do and learn about in L/D. It combines high tech with high touch, aka you really get to be there for your pt and make a difference in their birth experience. It can be a really happy place, but also high stress, and when things go wrong, it's really bad.
As far as high school classes go, take algebra, biology, chemistry, anatomy and physiology, genetics -- basically, take as much math, science, and health science as you can. It will help you *so* much when you take all these classes at the college level.
I'm not sure about training in a birthing center...if there's one in your area, go ahead and give them a call to see.
To be a Certified Nurse Midwife, you have to have a Master's degree. So if that's what you think you want to do, your best bet in college would be to get your BSN right from the start. That way you'll only have to go back to school to get your master's. Also, most programs require that you have at least 2 years of nursing experience before you start a master's degree program. It sounds like a long time, but it makes sense to get good at it first, before you become an expert in your field as an advance-practice nurse. It takes awhile to learn how to be a nurse -- I'm still learning the role, plus my job specific stuff (I graduated in May).
I hope some of this helps you. If you have any more questions you can send me a private message through this board.