a) it is safe to use account with lower access for security reason. However, it is recommend to enable the UAC so you may login as administrator but whenever you want to do administrative tasks , it will ask for your permission which is a safe method.
b) Using standard users you have limitation like for installing programs, accessing certain files and changing some settings in your PC.
c) You should have balance between security and ease of use and I recommend use UAC and you have to make sure keep your system update all the time. Take a look at:
https://learn.microsoft.com/en-us/windows/security/identity-protection/user-account-control/user-account-control-overview