Box 1: Yes -
The integration subnet can be used by only one App Service plan.
Box 2: No -
No Private Endpoint connections defined.
When regional virtual network integration is enabled, your app makes outbound calls through your virtual network. The outbound addresses that are listed in the app properties portal are the addresses still used by your app. However, if your outbound call is to a virtual machine or private endpoint in the integration virtual network or peered virtual network, the outbound address will be an address from the integration subnet.
Box 3: Yes -
Apps in App Service are hosted on worker roles. Regional virtual network integration works by mounting virtual interfaces to the worker roles with addresses in the delegated subnet. Because the from address is in your virtual network, it can access most things in or through your virtual network like a VM in your virtual network would.
Reference:
https://docs.microsoft.com/en-us/azure/app-service/overview-vnet-integration
