As far as I can tell, I did everything right - I made sure to unlock the bootloader and set up the phone again afterwards. Now my phone is stuck in a reboot loop - after holding Vol Down + Power it reboots and goes to the same screen regardless which buttons I hold. The worst thing is that now phone isn't visible to ODIN so I don't know how to proceed or go back to stock. I can't even turn the phone off, thanks non-removable battery! Any tips what to do next or did I buy a $430 paperweight?
EDIT: Fixed! What I had to do was:
1. Unplug the phone from the PC, restart the phone by holding Vol Down + Power
2. After the screen goes off, immediately hold Vol Up + Vol Down
3. Plug in the phone to the PC while still holding the buttons (do this quick while the screen is still off)
4. Press Vol Up on the menu to enter download mode
Now I'm back to stock, but at least I can try again doing it differently.