I would like some niche areas I should explore.

One of the problem is that although I have some github repositories showcasing some code, I haven't done any client work before apart from what my employer gave me. I am basically starting with a empty slate. How can I convince someone when I don't have other client's recommendations or portfolio?

If I was to build a portfolio, how many and how long should they take? Ideally I would like to start making money as soon as possible utilizing my experience.