You can check out gcaptain.com; they have some more of the "professional mariner" types over there.
In short no matter what you do, you'll need
a lot of sea time. I'd get a job as fast as you can working as a
deckhand, line handler, or something of that sort on a
boat somewhere. There are a lot of different options as far as
captain, mate,
engineer, radioman, etc. But for any qualification you'll need (roughly) a few hundred days of sea time. 4-8ish hours represents a day, but it doesn't mean 16 hours = two days, unless you were doing something like 6pm-6am, if you get my meaning.
You can even just drift on a
fishing boat to pick up some hours. Keep a log book
tracking your hours and have the registered owner or operator sign off on your time.
So no matter what you do, start clocking in sea time pronto.