It is no longer supported to use an enterprise admin or a domain admin account as the AD DS Connector account.
Reference:
https://docs.microsoft.com/en-us/azure/active-directory/hybrid/reference-connect-accounts-permissions

A virtual network is required when you create a NIC. Select the virtual network for the network interface. You can only assign a network interface to a virtual network that exists in the same subscription and location as the network interface. Once a network interface is created, you cannot change the virtual network it is assigned to. The virtual machine you add the network interface to must also exist in the same location and subscription as the network interface.
Reference:
https://docs.microsoft.com/en-us/azure/virtual-network/virtual-network-network-interface

Network Performance Monitor is a cloud-based hybrid network monitoring solution that helps you monitor network performance between various points in your network infrastructure. It also helps you monitor network connectivity to service and application endpoints and monitor the performance of Azure ExpressRoute.
You can monitor network connectivity across cloud deployments and on-premises locations, multiple data centers, and branch offices and mission-critical multitier applications or microservices. With Performance Monitor, you can detect network issues before users complain.
Reference:
https://docs.microsoft.com/en-us/azure/azure-monitor/insights/network-performance-monitor