Multi-Wan - Public Network

Situation:

I would like to setup a network as below without having to double nat multiple sites and having public ip’s on the other side instead of a local network. I read some policy based papers and realize that nat must be enabled for this to work but if the netgear decides to open a port (for its private network) i would like to avoid port forwarding on the 450 also.

What are my options as far as this goes - if it is even a possibility?

What is the function of the netgear?