That is catch 42! But married at 18 and planning a life together is so early...

 

My suggestion would be to try first to live together (no more long distance relationship - we're talking real life ;-) ) with a tourist visa. If then after 6 months (a long time when you are 18 ) you still want to go ahead, then work visa or marriage seems the solution.

 

1) You might have to get a 90 days visa that you can renew. You shouldn't have a problem to extend it to 6 months, after that it can bee more tricky.

2) If you are American, you do not need to get a visa for a tourist visit. You will need to apply for a visa if you want to stay longer and show that you won't be a burden for the society.

3) Don't know.

4) Always better to apply in person and to speak to them.