If I have more then one external (wan) IP address, is it possible to configure the RF600VPN so that I can use all my external IPs, (i.e. connect external IP 1 to my internal webserver 1 and external IP 2 to my internal webserver 2 and so on)?

Yes, you can configure multiple Wan IPs to the RF600VPN. You need to setup Aliases, DNAT rules and Packet Filter rules. Here is a setup example: