I'm 18 too, I don't have the hours you have, nor the vast opportunity in the immediate future that you have... I have 285 TT, no multi-engine time. I do have my CSEL cert though. How do you do it? Where did you get the funding for all that? I worked as much as a could with school, and a life and I still wasn't able to pay for all of it myself... Especially with that multi time.. You've got a hell of an opportunity, and I just think you need to realize how lucky you are. Hell, I'm extremely fortunate, but I worked my ass off for it.
I'll be quite honest, I've read, and read, and studied for about six months now... I havn't taken any of the CFI tests at this point. I'm actually scared of them, every day I doubt myself, I'm constantly thinking I'm not smart enough to be a CFI... But I'm sure as hell going to try. I stopped busting my ass for flying about a year ago though, it took meeting a girl that I honestly cared about. I always thought I was going to be the single-pilot through college, livin the life, yada yada. But she supports the whole flying thing, and it's fantastic(She even bought my tickets to Hawaii for my 18th birthday).
My point in stating that is that their are other things besides flying, it aint worth stressing out, or giving up your social life for. You're 18 man, It's sweet to be a pilot at this age but you need to be 18 too. Trust these guys when they tell you to take it easy, slow down, and go meet girls, and go to COLLEGE. They are older than us, and are much more wise than we are, that's a fact of life.
A week ago you were saying you wanted to move to Florida just to instruct? Now look at you, so what, you got kicked in the nuts by failing a written test. It's good for ya, shows that you're not perfect, and none of us are. I know most of the comments on here have been blunt, but they're all the freaking truth. These guys will help you as much as they can, if you really want it. At this point though, it seems like you don't actually want their advice, just their pity. They won't give it here, not for this. They've all been through it, and they're probably pretty skeptical of most 18 year old commercial pilots. And by the way your responding to them you're just reinforcing that skepticism. There's a ton of good advice on this thread, you just need to read it with a calm, collected, non-18 year old mind. You asked for their advice, and they all gave you it... But that remark of being a great pilot gave them the fodder they needed and wanted to give you a taste of humility.
And I really want to reinforce the point of going to college.... Go live a little, get back on your feet and do what YOU think is right for YOU.
I appologize for any errors, it's one in the morning and I've been up since five.
Also: If you really want to be a CFI or further your career more, you're going to have to work at it, a lot more than it seems you have. Our generation seems to have an issue with putting an effort into things even if they get something back for it.