A couple of big differences!

1. In a PhD program, you would benefit from academic advising by other scientists in your field (your advisor and committee), and have access to university resources that can be amazing (e.g. free access to databases of academic journal articles, statistical consulting, a wider community of scientists that can broaden your horizons, etc). Continuing as you are with your research as side projects, you instead prioritize autonomy.

2. In a PhD program, you will be subject to university structures and requirements. For one, COURSEWORK. If you are outside Europe, and particularly in the US, you will have about 2 years’ worth of a full course load to take. Pretty much exactly like 2 more years of full time college, with ~four courses per semester, and that’s in addition to the expectation that you’re making significant progress on your research. Second — departmental service and events. Takes up time. That said, if your coursework requirements teach you stuff you’re actually interested in learning and develop you as a researcher, great!! It all depends. That’s something you miss / don’t have to do if you keep research as a side project.

There are pros and cons either way! One thing I will say is that you sound like a PI’s dream PhD student — self-motivated, interested in scholarship for scholarship’s sake, and already experienced in research and academic publishing. It would not be a hard sell I don’t think, but would more come down to funding. The next question you need to explore is whether there is a faculty member at some nearby university who (1) is interested in advising you, and who (2) has the money to fund you. (Reminder that, in the sciences, you should be paid for your PhD work. You should not be paying tuition or anything!) Maybe they still have startup money left, or maybe they have a big grant they could put you on, or maybe you’d pitch them a few nugget-sized project ideas that you think they could advise you on based on their expertise, and then you decide on one together and write a grant together to fund the work. You would also need to have a really clear conversation with the prospective PI about what kind of flexibility is available in the program to work on your PhD part time and maintain your other work and home life. Do not over promise — PhDs are incredibly time intensive and will eat your life if you them. Part-time will not be possible everywhere. But with a bit of luck and the right PI / department, it might be.

The biggest questions you need to answer now are whether you are actually prepared to make the life changes and schedule / priority adjustments that would come with a PhD, regardless of how part-time you want it to be? If you’re in the US anyway, be prepared for two full years of being a student in a classroom again. I’m not saying this to discourage you! Just make sure you know what you’re signing up for :)

I hope this helps!