What is the UID the root user? What about a regular user?

UID of root user is 0

Default values of UID_MIN and UID_MAX in /etc/login.defs UID_MIN is 1000 UID_MAX is 60000

Actually, we can change this value. But UID < 1000 are reserved for system accounts. Therefore, as per the default configuration, for regular user UID starts from 1000.