Initial network connection setup in SAP IS or APIM or SAP Event Mesh

Hello Experts,

We are planning to migrate PO to BTP (SAP IS or SAP Event Mesh).

I know that we need cloud connector to connect on-premise system to connect to SAP CPI , Do we need Cloud connector also for on-premise system connection in APIM or SAP Event Mesh?

How about connection setup when we wanted to connect to Cloud based systems in SAP CPI or APIM and SAP Event mesh? Please let me know also how to find out SAP CPI IP address to share to our partner systems?

When does Firewall comes in to picture ? When do we need Whitelisting ?

Could you please help me to understand clearly the initial network setup required to setup connection with Cloud based systems or on-premise systems? Please let me know the prerequisites required.

Thanks,

Ramu.