Okay, I got it working with a fresh installation. It guess it was important to add an internet connection during the installation. There were some packages downloaded/updated which seem to be required.
Also I choose “don’t set up anything” on the second installation step.
Then I ran sudo /usr/libexec/initial-setup/initial-setup-graphical and my computer was shutting down during the network setup step.
Rebooting with qubes.skip_autostart works and I can start a qube and access the internet now.
Now I set qubes.skip_autostart for linux and x2apic=false for xen via (Custom kernel options/parameters not used - #5 by dipole).
Reboot is working without modification of kernel options. Updating VMs is working, updating dom0 is working via command line.
So I guess it’s okay for now?