RH ACS Documentation provides minimum persistent storage size requirements for Central DB, Scanner V4 DB and secured cluster scanner V4 DB.
https://docs.openshift.com/acs/4.5/installing/acs-default-requirements.html#default-requirements-central-services_acs-default-requirements
Central DB - 100GiB
Scanner V4 DB - 50GiB
Secured Cluster Scanner V4 DB - 10GiB

It would be very beneficial to provide some minimal storage performance metrics here as well (IOPS, Bandwidth) as I know couple large customers who experienced issues with ACS Central performance and stability due to inadequate storage assigned to Central DB PVC (1000 IOPS and 1G bandwidth was not sufficient).