Income will vary depending on your location, industry, what you are actually doing (IE designing the site vs designing art) and how long you've been doing it.
I don't have much experience in web design but I have a cousin that did do web design for a Wal-Mart for a while. She had a degree but she ended up doing a lot of specific icon creations - it wasn't really web design, it was more art work on a graphic level.
So to answer your questions as best as i can:
1. What you will be doing depends on the job you get - web design can be anything from structuring a website, PHP and C++ coding, aesthetics to designing the icons and pictures shown on the website.
2. Income varies man, just like anything else. My google's shows that the average income is around 60k a year - but that depends on a ton of factors. Considering you have zero experience I would think you would probably be in the 45k range.
3. I would get an associates or bachelors from an accredited university in web design.
