It says to give it a public IP because otherwise there is no way to ssh to it to configure the appliance. If you setup a jump box in the VPC and then ssh from that to the CloudBoost appliance you can probably avoid the public IP requirement.

I am not sure what you mean by backup option. Perhaps you are referring to how the appliance does a DR backup of itself. If you have a more specific question I can attempt to give a fuller answer.

Correct we are accessing it via a VPC jumpbox - however I cannot get the EMC Cloud Portal to "activate it correctly"

The appliance will need port 443 access to console.dpccloud.com outgoing but it does not need a public IP. Most likely there is a security group rule blocking access to the portal.