4 Hosts indicates that you have ESXi standard or better..... so as soon as you add your new ESXi Hosts to the existing vCenter you can use
1. Storage vMotion to migrate vCenter to the new Hosts as long as EVC Mode match
2. use the Clone feature of vCenter and create a Clone of the current VCSA. After that shutdown the original and start the "clone" on the new Host/Datastore. To reuse the the oringal VM name you should rename your existing vCenter to VCSA_OLD first and than start cloning.
3. Backup and Restore
When you say backup and restore?
Than i mean to use your VM Backup software and perform a restore of that particular VM into the new Host/Environment.
Another solution could be to use Veeam "Quick Migration" which is a Veeam backup & Replication (free) feature:
VAMI backup/restore is one option.
You can use scp protocol and take back up on one of the ESXi host. (like: scp://<ESXi-IP/FQDN>/vmfs/volumes/DATASTORE/backup)
Power-off the source vCenter server appliance
Mount the same build iso and restore. You can choose destination host during the restore wizard.
I'm assuming there's IP connectivity?
You'll most likely have to upgrade the vCenter version as SimpliVity will be at 6.7 I'd have thought. So upgrade vCenter, then add the SimpliVity nodes, the vMotion but do a storage vMotion as well.