I have finally compiled my own build. Everything seems to be working fine. I had to remove the camera modules to encrypt my phone (the phone is crashing upon reboot with the new camera modules).
Performance is great! The animations seem a little smoother that on 14.1 which makes it pleasant to use.
I’ve downloaded F-Droid and couldn’t launch the APK installer somehow. After moving the APK to the external sd card, I was able to install it without any issues.
Encryption works (as described by @AnotherElk), I can confirm though that TWRP cannot deal with the encryption (I’ll try to get some debug information on that later).
It takes some time to get used to the new icons and menus. My favorite feature so far: Being able to change the font size and display scaling. I have reduced the size of everything just a bit, which gives me a bit more screen space.
EDIT: Forgot to mention that dual SIM works great now! Thanks @chrmhoffmann!
Here are some screenshots from the initial screens (changed the wallpaper and the theme to dark):