First time WAN hook up at remote location. Need some help.

Hey everyone,
We are setting up a new LAN in remote location. I need to clear some concepts. I am setting up a 192.168.90.0 addresses on that LAN. Now I wanted to know the IP addresses on our Cisco router interfaces. The ISP has given us a WAN IP which I will set up on CSU/DSU interface. Then I also got two public IP addresses for Router and the Firewall. Now do I need a 192.168.90 address on Cisco router? I am planning on putting the Public IP that ISP has given us on eth0 interface which will connect to our firewall which in turn connects to a switch where all the equipment will be hooked up. DHCP on firewall will give out the 192 addresses to devices.
Thanks for your help.