Self IP for External VLAN on Active/Active Configuration

Hi Experts,

I want to implement active/active configuration using two BigIP 4200. My plan is to put both device to host my web server without firewall in front of them.

My questions is :

1. Do i need self ip for External VLAN on each device? I really don't want to waste our public ip.

2. Suppose our web server will accessible from both public and office network, do i need to create 2 VS or just one VS (put it on DMZ VLAN) and redirect traffic from public ip using NAT?

Thanks guys...