Frequency of SQL DB Full and Differential backups
The backup policies are actually based on your RPO. But here is my suggestion.
 Use Ola Hallengren's backup script.

If your total size of the DB is &lt; 1 TB


Full Backup - daily 1AM - Retention 7 Days
Differential Backup - Every 12 Hours - Retention 3 days.
Log Backup - Every 15mins - Retention period 1 day.


If your total DB size > 1TB


Full Backup - Weekly once
Differential Backup - Daily once/twice (Based on the database load)
Log Backup - every 15min/30mins