What are you goals? If you're just looking for someone to read your stuff, it might be a useful site?
Why not? If you have your stuff somehow copyrighted (just to be on the safe side), you got nothing to lose by uploading a chapter or two. I view it as free promotion. Why not? Just don't forget to mention it right from the start that you are only uploading a sample. It's respectful to the readers. At some point, I think that I'll be doing the same. I crave some love from readers, since so far the only two people that view my work from time to time are heartless sadists.
Mainly, yeh. Its no where near completion yet although the first few chapters are pretty much ready. I want to start building a following and generate interest for when its complete.
I think that it's best if you waited until you're finished with it, or at least when it's nearing it's end. If you are taking it seriously as a promotion medium though, do not make the same mistake everyone else there does. Do not upload a rough. Upload the edited, finished writing.
Your work is "copyrighted" the moment you create it, at least in the U.S. and U.K., and many other countries (Berne signatories). If you're in the U.S., a registration makes sense within three months of your publication date.
From what I've read (as I said, I didn't spend long on the site...) Wattpad isn't the right place for that goal. The people there, on the whole, aren't interested in giving free feedback or being marketed to: they want free, entire books. By giving them a few chapters and telling them they'll have to wait and pay for the rest, all you'll do is annoy them. I think many Wattpad users won't even start reading a novel until it's all on the site, having been burned. This is second-hand info as I said.