I'd like to host redundant internet accessible (NATed) web servers behind a f/w on the same standard ports. If I only have 1 publicly available address do i have to use a reverse proxy or load balancer? If I can get more public address space (and not NAT) do I have to subnet that space to make it routable?
Yes you would need to have some sort of load balancer
Along with some sort of file replication and database replication.
Depending on windows or linux there are software load balancers that can be used and assign a Virtual IP for the load balancer
You can then NAT that address on Port 80 and route traffic to each server.