I finally quit my job, want to start on my own. What do I need to know?

Been in software engineering for more than a decade, lately in senior positions in big companies, w/ experience in large scale projects, data/machine learning, people/project/product management. The past few years became less fulfilling, and as a project I was on got cancelled I finally called it and stepped out instead of moving to another project.

It's been a few months, living off my savings, no family. I've been hacking away at some old ideas and pet projects, and eventually one will stick. For now, my end goal is a small-scale operation that pays the bills and requires minimal maintenance, and can be built by just me to start, perhaps within a year.

At big companies, there's a lot that's taken care of for you behind the scenes, and outside that environment I don't know what I don't know. Hence the question. Thanks.