If I understand right your question, then you are asking where to configure your public IPs on the Router or on the Firewall.
Well that depends basicly from your public IP Range and how many of them you need for NAT.
Option 1:
Split your public IP range (Subneting) and set one public IP range one the outside interface and the other one on the Inside interface.
Then set a public IP on the Firewall and set the router as default gateway.
Option 2:
Do all NAT on the Router. Configure the public IP on the Routers outside IP. Then choose a free PRIVATE IP range for the inside interface. Add a private IP on the Firewall outside interface.
If that does not answer your question then please give me more details.
sincerely
Patrick
