You can have 16 disks per SCSI adapter. So if you have SCSI Controller 0 for your non-shared disks such as the boot disk you could have 3 additional SCSI adapters for shared disks with 16 disks on each adapter.
You can have these for each VM, i.e. you can configure scsi device 1:0 on multiple VMs all pointing to different virtual disks.