Hello,
1. First Install you HANA system and activate the MDC
2 then When you install ERP, you will create a new tenant.In the SAPinst you will have the options to do so.
3. Do the same for the other systems.
The System DB is not used for Application. Each application must have its own tenant.
The SystemDB is there to manage the system and the different tenant.
Hope this helps.
Best regards
Guillaume Bruyneel