What do we need to start working as a web developer?

I've been meaning to start working as a web developer for some time now. I studied programming at colege and I never finished my career, but I've continued to learn stuff and want to follow this path. Even though I've done some easy/quick jobs, I don't really know what's the point where I can go out to the market and say "Hey, if you want a website, I'm your guy". I'm really worried about clients asking for something I don't know, or something I think I know but I don't (That's even worse). So far I know programming's logic, html, css, I know some SEO, I'm learning javascript and I know how to use wordpress. I still plan to learn more and expand the tools I can use. But, in your opinion what is the minimun a web developer should know before starting to work with clients, or in a company? Please, if you may, make a little list of those things, I would really appreciate your opinions too.