Same Subnet VIP/Pool

If the traffic is coming from and being load balanced to the same network segment, then you only need to configure a single interface/VLAN (in your example, VLAN 4). This is what F5 refers to as a 'one-arm' or 'one-IP' configuration. You didn't say which version you are running, so this may not be the correct implementation guide for you, but it should give you an idea of how to configure for your situation: LTM Implementations: Configuring a One-IP Network Topology.

You need to pay special attention to how you configure SNAT behavior going forward - without a SNAT, the host you are forwarding traffic to can reply directly to the source of the traffic, which will result in connections being reset by the originating host. Again, this may not be the correct manual for your version, but have a look at this information about SNATs: LTM Concepts: SNATs.