I think deep down you are the only person who knows whether you should do a PhD or not. I would just say that it does sound like you think you should already be on the career path. I can't say whether you'll be happy as a quant - I can say that it sounds dead boring to me. I can also tell you from my own experience, changing careers mid-life is really difficult despite what the internet says. It's not just a question of good grades etc. People will ask what you'v been doing for the last X years and if you can't make it relevant it matters not. You may as well have spent them on the couch.

On the other hand, I think the economic situation will only get worse as the developed world's demographics continue to tank. When the boomer generation liquidates their assets in two or three years, the party will be over. I think most academics and PhDs/postdocs are woefully unprepared for this reality. That said, in these situations finance jobs are also some of the first to get axed. The truth is a real economic nightmare, which hasn't hit yet, it will be skilled jobs not desk jobs that pay for the most part.

Sounds like your supervisor is really unreliable / unmotivated. Quitting sends you back to Square 1 though. It also sounds like he has expectations on you that you were not aware of, but that's not necessarily his fault. You need to fix the communication, that's for sure, and find out why he has been ditching meetings. You can't rely on him to put things right. You also need to discuss the research themes and tools. If you need to use databases, then you should have definitely known that, but that's not necessarily your fault either.

I think you can ask potential PhD supervisors directly if they would consider a distance learning student, or at least allow you to work mostly from home, as you probably will have to go to the university at some point anyway.
This arrangement was offered to me right off the bat by one professor I spoke to, but that was a computer modelling project which didn't require a lot of time in libraries, archives etc. I don't know if history would be so easy.
Also it sounds like you should do a master's degree first. I would recommend this to anyone prior to looking for a PhD.

I was offered a PhD position which required the student to carry out shift work in a government-run physics lab. The compensation was $800 per month. Not great but better than nothing. In this case the work was not directly related to the thesis, but students conducting thesis work in the lab were expected to put in time to help run it. At the end of the day, if you value your work you should inquire about compensation. But as you say, politely :)

Hi,
with your grade you should definitely apply to a few universities, I think you will be ok. However you are towards the lower end of "good" (I'm not judging, I was the same). As you probably know, the numerus clausus process means that there is generally no qualifying grade required but places are limited. The average entrance mark for Masters is often quoted as being 2.5, whether this is true I don't know. But with a 2.4 I don't see why you shouldn't apply, although for the more popular universities you may have to sit a suitability test.

I can't say anything about TUM or Berlin, except that there will be more applicants than places obviously. My advice would be to absolutely apply, but also find some alternative universities to apply to as well.

It should be ok - there was a guy on my MSc who had graduated about 15 or 20 years ago. The department insisted he work part time on the degree. I think in his case it's what he needed. So it wouldn't surprise me, if they interview you to see how much you remember. Good luck!

Hi, I also did my undergraduate in physics in Germany, and although I left I did explore a lot of graduate options there. I'd say only that whether you leave your well funded position in HK is up to you of course, but if you return to Germany then consider doing your PhD there as well. The funding opportunities and research are amazing compared to many countries and because you will have completed your pre-doctoral studies in their system, the application will be straightforward for you.

Use the time during your masters to attend seminars, summer schools, conferences etc at other universities and you might find the right group for you.