Restart. Some updates. Mac does not start anymore. Logs attached. How to fix it?
The crash report blames the installer, so the installer ran into a situation it could not cope with.

Can you boot into safe mode (Shift) during startup? If so download the combo update for 10.13.4 and run that.

If not, then the big question is can you boot into recovery mode (⌘r) at startup?

If you can I would first run disk utility and see if it can repair the disk. If it reports errors that can't be fixed, you have a problem as I am not aware of any 3rd-party disk repair utilities that can repair APFS disks (anyone?). 

Please tell me you have a current backup that you can restore from?

If not I would be tempted to take it to an Apple Store and see if they can do anything with the drive.

If Disk Utility can fix or finds no issues, I would reinstall MacOS from Recovery Mode. It shoudn't wipe any of your files but depending on what happened I could not guarantee that.

That should get you started.