Nick gave you some good advice, but I think what you really need is to find someone who can help you with all of those items and more. Since you don't even know how to start, it's going to be a lot for you to learn. If you have the time, that's great, but if you don't have the time or the interest to learn all that you need to do, working with someone may be the way to go.
A more simple approach may be to get a Yahoo store. You may have to pay a little more to get your site up and to keep it running, but Yahoo makes it pretty easy to get what you need running. The thing they don't really provide is much help with marketing and promotion.
I suggest you find some ecommerce or business forum sites, learn as much as you can, ask lots of questions, and then when you feel you understand the basics, or find someone to help you, then jump into it and give it a try.