Hi Jonu Jay,
Now that is tricky.
You need to make sure HANA secondary site shall remain active with pre-loaded data and also has some resources to keep accepting the data. So that is completely on your production server.
You need to take care of:
Current database size(because that will be there in-memory)
+
growth of database(because it will keep increasing depending upon the throughput of primary)
+
Resources required to do the replication.
There is no such measurement tool which SAP provides to calculate the "how much it should be set to after the initial load is completed."
In your scenario I suggest is you shall restrict your DEV/QA systems and not secondary HANA system which is being replicated.
Happy HANA 
Deepak Chodha.