Ask HN: Considering a Paying Side-Project

I may have the opportunity to inherit a full-stack project I previously worked on that can support a partial developer (.1 to .2). There's one customer who uses it and wants to continue to use it, with some feature development now (which I think can be done in that .1 or .2 timeframe). I have no ambitions of growing it as a company, just keep running it as a side project. If I take this on, what are some things that I should keep in mind?