Pre-Military/Coast Guard Questions & Advice?

[Caz]

Female, 18 years, 2nd semester of college.

I'm considering joining the Coast Guard, but I want to have some schooling before. So some questions for people who're military experienced:

1.If I decide to join the CG, how long would you recommend I go to school?
2.During this, are there any courses I should take?
3.What can I be doing to get physically ready?
4.I wear glasses & need them: ESPECIALLY at night. I usually swim without them on fine, even underwater in a pool without goggles. Will this be a problem?

I'm naturally very skinny. I want to go ahead and get started ahead of time, b/c I know that training is probably one of the hardest things I'll ever do. I'm not a strong swimmer, so I'm going to start working on that. I'd like to be a HS or PA someday. But I'd be happy doing other things too.
I want to do this b/c I love my country & want to serve it & help people too, though I don't know if I plan on making a career out of it. If experienced people could answer these, thanks!