Getting a funded PhD vs starting up my own research idea
Signing up for a PhD is definitely a huge life investment and I am glad you're not taking it lightly. I am getting mine in biological sciences, so we are similar in the length of a program, the funding mechanisms, and the publishing realm. I can't speak from experience of a masters program, though, or from computer science.


When you are getting your PhD you're working with an advisor on their funded projects. Now, that does mean that you are becoming an independent researcher, but I argue that it does not mean that I have not been contributing my own ideas. I am very involved with my experimental design, data collection, and spin off projects. It is like you pick a lab/advisor with a "theme" that you like - and from there, you can develop aims that will complement their focus, but are your own "flavor".
Many funding mechanisms require that you are employed by a university/government/company. Here in the US, this is shown by a DUNS number on your application. Since I have experience only with a university, I do not know of funding mechanisms/grants that are available for those who are not "in the system". Additionally, to get the rather large grants, you must have a PhD and gone through the tenure track.


I have a bit of knowledge of the "spin off" business side of things through a few classes, which makes me wonder maybe you are a great candidate for starting your own company. You could get funding from investors, still work on your own projects, and contribute to the community. 

In my field (biological sciences), academic journals would very rarely, if ever, publish you in high tier journals as a MS without a PhD as the corresponding author.

Good luck - I can't stress enough how much I respect you thoughtfully considering your career path this way. I am confident you'll make the right choice for you.