In the end I "just" wrote a new blogging software for myself.
I have no intention in publishing it, because there are so many blogging engines out there, that you don't need another one which only barely fits your own requirements.
Lessons learned:
- You can't rely on any free service on the net.
- Nothing fits your requirements 100%.
- Customizing existing blogging engines is as much effort as writing one yourself
- You don't need all the features.
And again: Sorry if the feed shows old posts as new.