1) not 100% sure of your network, picture might help. but you have a firewall interface and the f5 self ip in the same subnet with some servers and the servers can exit the network via the firewall but not the f5? that is by design, look at virtual forwarding server to setup routing on a BIG-IP.
2) why without SNAT? anyway you can just put a virtual server and load balance to to public IPs, as long as you virtual server have the default gateway set the the F5 the traffic returns.
3) i leave this one for another, little experience with WAN optimization.