Hi @Azy1
If it were me, I would take the following approach:
1) Use the CIDR of the VPC, unless you want to tunnel all of your traffic out of AWS(?)
2) The KB you are looking at shows some tools that you can use to monitor the performance/stability of that VPN and alter the VPN preference accordingly. If you are struggling, I would focus on getting the primary up and running first and verify connectivity. Worry about the failover afterwards 🙂
Tom
Technical Solutions Architect, Meraki
CCIE #67185