Alternatively, you can use a distribution service. I run Book Hatchery (www.bookhatchery.com), a web service that helps authors publish their books digitally. You can sign up for free and we'll format your book and get it listed on Amazon, B&N, and Apple. We also have a paid plan at $25/mo that provides you ISBNs (which normally cost $125 and required by Apple and some other ebook retailers), print on-demand help, and some other features. We are a startup working with an alpha product, so our service is constantly evolving. Of course we'd like all of the feedback we can get, especially from authors :)
Also, regarding question #2, that choice is up to you. For most authors selling ebooks you can simply operate as a sole proprietor (no fancy/expensive legal work required). If you ever make some reasonable money from your books you might consider forming an LLC.