Prosafe VPN / FVS336Gv2 / Windows 8 setup

I've just run into this combination of devices / software (which I didn't set up) and could use a few pointers and resolution to a particular problem:
- The router is a Netgear FVS336Gv2 and I suspect there are no issues with it. But maybe?
- The clients are all using the Netgear Prosafe VPN client software. Some are Windows 7 and some are Windows 8 / 8.1


All of the clients have to turn off the Windows firewall for the VPN to work. I need to fix this.
Is it typical to have to open a port on a Windows client?
If so, which port(s)?


How are the client IP addresses managed? I see that each client can set its own IP address for the client end of the VPN which is separate from the client end network subnet.
How are these client addresses usually managed? By communication and agreement? or....?
Do these addresses have to be set up in any way on the router?


The objective, common enough, is that they need to get at files in the main office.
From a Windows point of view I see that the VPN network connection is categorized as Public. Is that normal? If not, how to make it Private? or ..... ?
Public mixed with firewall questions often seems to cause problems if not just confusion....


TIA