Yes please, always do backups before you change important things on your system.
Make sure you run NC 13, since NC 12 does not support php 7.2. There have been a couple of issues regarding the setup of php 7.2 but it was related to how the system handles such upgrades and not issues with NC. Feel free to check the php 7.2-tag (I added one to your topic, just click on it to see other topics).
Jep PHP7.2 working flawlessly here on my NC13. But it also depends on the used apps, I guess. According to some research I did some months ago, PHP7.2 has some performance advantages over 7.1. Anyway moving back to 7.1 e.g. is really no big deal in unexpected case of issues. Backup of course should always be in place.