It doesn't sound pretentious, it sounds like fun =P
It also sounds like one hell of a fun life. Go for it, I vote, and that way even if you do fail, you're not going to regret giving up on your dreams, are you? I think if I was in your position, I'd regret losing those more than having lived a life of just drifting around.
Good luck, okay? (I bet you won't need it though)
And I think careers would only be like that if you were forced into them, or if you were in one that you disliked, or it didn't suit you, I guess. I'm hoping that someday I'll stumble onto something that I find interesting enough to stick at, although I'm starting to think that it's not going to happen =/ I bet I'll end up drifting around, sooner or later...