The NSX Public Cloud Gateway (PCG) provides north-south connectivity between the public cloud and the NSX-T Data Center on-prem management components.
Your public cloud accounts must be already added into CSM.
The VPC or VNet on which you are deploying PCG must have the required subnets appropriately adjusted for High Availability: uplink, downlink, and management.
PCG deployment aligns with your network addressing plan with FQDNs for the NSX-T Data Center components and a DNS server that can resolve these FQDNs.
It is not recommended to use IP addresses for connecting the public cloud with NSX-T Data Center using PCG, but if you choose that option, do not change your IP addresses.