I may be able to contribute a bit. I have a 3B+ and use the built-in BT to connect to a Logitech Audio Adapter which feeds my stereo. On first attempts using VLC, audio was horrible, mostly silence with occasional blasts of sound - severe stuttering to say the least.
However, using either mpg123 (for mp3s) or aplay (with wav files), sound played fine, ...
All that leads to behaviour specific error related to OS version (Voice HAT on Raspberry Pi). Problem with sudo not playing music was resolved after installing pure "Raspbian Stretch Lite" and adding all necessary drivers.
To answer my own Question at least to a small extend:
VLC seems to offer a something similar to pygame but with the advantage that (to my knowledge) no screen is needed and it plays pretty much every data Format.
Here a quick link: https://linuxconfig.org/how-to-play-audio-with-vlc-in-python
As for the code, Iam still greatful for every advice, especially ...