I've been trying different ways to try SFOS, but have been failing. I installed multirom first but after failing to get it running as a secondary rom I decided to wipe my phone and flash cm12.1 + sfos beta 5 as main (and only rom) but times ended during boot stuck at google logo for over 30min.

I wonder if this is a kernel issue. I had a android 6.0 variant installed before and wonder if that could be an issue even when I just installed sfos

Perhaps you should use CM11, like instructions says ?
https://wiki.merproject.org/wiki/Ada...for_hammerhead