Flickr & DeviantArt are good. DeviantArt lets you sell you your images, as does Redbubble. Flickr is good in that prospective photo buyers look at that site for stock photos, but don't expect to get rich doing it that way. Photography is an extreamly competitive business, but there are lots of ways to make money in it. It always helps to shoot things YOU really enjoy shooting.
Names are difficult. Most folks just go with their own name, but if that doesn't work you've got to find something that defines the type of photography that you want to do.
Watermarking is different from copyrighting your images. There's lots of info on how to copyright images and one of the cheapest ways is to copyright a whole CD or DVD, but there is a time limit on doing that and having photos published on the web.