Ask help to choose a backup strategy

Good afternoon,

I ask help through your experience to choose a backup strategy.

The organization uses Exchange 2013

CAS01-03 – CAS Servers

MDB01-03 – Database Servers using DAG

Just one Database (800 Gb) in DAG and one Archive DB (400 Gb).circular login disabled, deleted items save 90 days

CAS01,MDB01 – City A, CAS02,MDB02 – City B, CAS03,MDB03 – City C

DPM make two backups per day, save point one month. Backup DB from MDB01,02 and 03 servers

I think the backup is done too often.

I intend to:

Analyze how mailboxes grow for some period. Get mailbox statistic for the week.

Create two or more mailbox DBs

Move user mailbox, which has not increased during the week, - to DB01. And other, whose mailbox has increased to DB02.

Create new backup schedule for DB01 two days per week, and for DB02 one copy per week.

What do you advise?

Is it worth it to keep the circulation of disables? Are they needed for a differential backup?

Thanks!