Update.

SW
I have now achieved writing a service/daemon which is on D-Bus systemBus, and managed to configure policies so that it can own a name and be communicated with. Also configured systemd to start it at boot.

Now i can access the rear I2C bus and V33 output through D-Bus from normal application without starting it as root.

HW
I think i will do board as FPC - then i can keep height in minimum.
Thickess increase should be ~1.5mm, which is thickness of OLED glass.