You sound a lot like me when I was thinking about doing a PhD, albeit you aim to be a professor, and while I like the idea I'm not so fussed about the administrative side of being in a university.

If you have a tendency to concentrate on whatever is the most interesting thing in front of you, then I would very strongly advise proceeding if and only if you find a good, hands-on supervisor. Ask their previous doctoral students how often they met with them in the first few years - some supervisors will see you once a month or so, others I have heard meet their students individually or collectively several times a week.

In the UK, PhDs are usually 3 years. And the rough schedule is that for the first year you look at one or more problems, trying to understand how you might make some progress. In the second year, you make some small advance on one project and try in vain to develop the project into a more concrete thesis. In the third year you accept that your small advance was all you are going to get, and write it up. The slow pace of progress in the second year commonly causes distress or apathy.

In order to complete such a project, you either need to be personally very disciplined or be part of a team (you, your supervisor, perhaps some peers) that can keep you honest - remember that rubber-ducking is a vital part of academic work; most academics in the UK will congregate in the department kitchen once or twice a day just to talk to other academics, because often just explaining yourself gets you closer to a solution. Similarly, you need people to ask you where you've got to so that you don't just disappear off for a month because you're faced with something annoying and your symphony suddenly seems fascinating.

I struggled with this; my supervisor was hands-off, my peers were in very different fields (I was a theorist among experimentalists for a start) and I didn't really understand my own character enough to see what was happening.

One of my peers had a supervisor who used to take students through rigorous textbooks, and expect them to grasp whole chapters to be quizzed on - the sound of it terrified me, but in retrospect the foundations are well worth laying. Instead I often disappeared down dead-ends because I was unaware of entire fields of research, and just didn't have the terminology or context to find them.

So, in sum, you have some well-placed concerns, but the answer is not just whether you are capable of a PhD but whether you are in the context of your supervisor, peers and department.

Who should pursue a Ph.D degree?
Does every floor contain a secret room (entered via bombed wall or having X-Ray Specs), including the Womb and Sheol?
