No. Oracle has predetermined the configuration parameters that work with the Site-to-Site VPN service. Your Site-to-Site VPN can't be established if there is a mismatch.
No. You must initiate it from your end.
Yes. IPv6 is supported.
No, FastConnect and the Site-to-Site VPN are two different services.
No. Packets from the VCN have the private IP address of the instance as a source IP address. Oracle cannot change the source IP address to the private or public IP address of the DRG.
Yes. Traffic for all the subnets in the VCN attached to your DRG is routed over both tunnels.
You can have a maximum of 100 tunnels from a unique CPE IP address per region. If you want more than 100 tunnels, either use a different IP address for the additional ones, or use a different CPE device (recommended).