I've set up a VPN tunnel between two locations successfully.  I used 2 Watchguard Soho 6 tc's.  Now, I'd like to add a third location using a Watchguard Edge X50.  Watchguard tells me I should have no problem doing so, but I'm wondering if anyone out there has done so, and could prepare me for any possible pitfalls.

Also, this new location will be connecting to the internet in a different manner than the first two.  I hadn't been worried about that until the salesman for the ISP mentioned it- he says they run NAT, and "will I be OK setting up my tunnel from behind NAT? "  I can purchase a public IP from them, but do I need to?  They want $25/mo for an IP.

Sorry if I missed anything- I'm new at this.

Thanks.