Global rom is certified. Sometimes after update u need to wait one two weeks for certification
Edit: sorry. Global stable;) Dev is, was, will be uncertified
Cache with dalvik wipe should be enough but in case of any issues wipe all.
Do it via TWRP. I don`t trust updater app :D Dissapoiointed me few times.
OFC full backup first ;) via TWRP too
Wait till night. It should be another update so why to updating twice