Like, I'm not sure how else I could publish my books/stories and actually make any money off it. I think there's a few other similar sites that allow you to sell your work (and even charge to allow people to read beyond a certain point, but I think that's a touch scummy to be honest) Keep in mind, I mainly just want to get my project out there and read. If and when I decide to sell it I probably will, but I have no idea what the full process is.
You can do that, but you are essentially throwing your first publishing rights away. There have been some Wattpad success stories (no pun intended) though. If you have no interest in getting a specific piece traditionally published, then it probably doesn't matter. There may be other considerations but I'm not knowledgeable about them.
I agree with Bruce that if you plan to go traditional with the story later, it might not be the best thing to do. It's hard to sell a book to publishers that's already been published. However, if you don't plan to send the book to publishers (and instead want to stick with self publishing) then I think it's a pretty good place to get started. I've seen a lot of authors get their start there. There's a book in the top 50 on Amazon right now that was originally a tumblr story and I've known a lot of authors who took their wattpad story down and republished it on Amazon with really good success.
I might do that then, publish the thing on wattpad to get it out there and get some feedback (hopefully within a year or so) take it down, go through the whole editing circus (let's not mince words, it kind of is one when you want to publish a thing heh) and then publish on Amazon.