It varies but most of my servers do a full System State and all change data nightly . They go to a local Storage Server and then offsite. As for the DC's I was doing NTbackup nightly and then copying the backup nightly to a NAS with EASEUSE TOTAL BACKUP.
All servers are cloned to the NAS monthly and all change data backedup nightly. Then I backup the NAS data to Hard drives that go offsite weekly.
My high priority client data is backed-up with Evault/i365.
I think your backing rotation for 150 users is suitable, just be sure to double check that the back ups have been completed successfully after updates, Depending on your OS's build backups can have a fit in conflict with updates.