I am omnivore, having successfully maintained both outdated Eclipse/OSGI-based codebases and large PHP websites, but everyone wants to buy me in entirety.
Being freelancer is more difficult for the not long term, but the best to achieve shorter working hours I would say is, work full time for 9-12 months, then you know how things work and also have some "power" to request part-time.
The problem of course is that after 2-3 years you will most likely change job again, so it does not last too long as long as you want higher salary
Honestly, I'm content with being in middle class but I also think about future opportunities and work towards bigger goals.
It's about 8.7% in North America according and 2.7% in Europe to Credit Suisse[1]. That is not _many_, that is _very few_ in my dictionary.
[1]: https://en.wikipedia.org/wiki/List_of_countries_by_number_of...