Setup question: WAN Router & vpn / fw-router+++

Hi all...

I have this simple setup question that I'm trying to understand.


Scenario

Site A:
----inside network----[fw router]-------[wan router]---T1--internet




Site B:
----inside network----[fw router]-------[wan router]---T1--internet


I'm trying to understand how IP addressing work in this setup, where I
am looking to establish a VPN/IPSEC tunnel between the FW routers of
Site A and B. Also, the FW router will be doing NAT for remote user
vpn dialup.

When ordering internet connection from telco, do I ask for 2 public
subnets for each site? (one for wan router to internet and other for
network between fw-router and wan-router) That way the fw-router will
always be reachable via internet so vpn can establish?

Any thoughts or insights would be gladly appreciated. Thanks.