The address is the one you are putting into the port forwarding section, this is the address you are talking about. If it is it should be the address you are using or your vpn is using to serve from your side/your computer. So this should be your IP address of your notebook that is serving your side of the vpn, I would think this but I haven't worked with vpn much. This is what the router is asking though when it says server address, not the address of the server outside of your LAN. IE server address equals local server address which is the address inside you local area network that is serving up the files. Inside your local area network/LAN is anything connected to your side of the Netgear router.
From your manual you should be able to open up the Ipsec port 500 and the port 2001. As far as the protocols of 50 and 51 then I don't think the router has specific settings available but as you said hopefully the firewall will handle it automatically.
As ZX10 said though the vpn would not be working if all was not ok. You might check the UPnP section of the router as it may have these ports already open through the OS, if it is enabled UPnP then it actually should.
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