Load Balancing Question

Your configuration is refered to as BigIP-on-a-stick, or classically vip-bounceback.

Clients should hit the VIP, say 10.10.10.250:80. BigIP will need a snat (which can be defined in a snatpool, or simply select snat automap) applied to the virtual server if the servers are in the same subnet. The reason this is so is because if the F5 is not the default gateway and the traffic is passed with the originator's IP address as source, the servers will send the traffic directly back to the client, bypassing the F5. This is OK on some protocols, but not TCP, it will break. A configuration like this should work for you:

virtual iis-vip {
   destination 10.10.10.250:http
   snatpool iis-snat
   pool iis-pool
}
snatpool iis-snat {
   member 10.10.10.250
}
pool iis-pool {
   monitor all tcp_80
   member 10.10.10.252:http
   member 10.10.10.253:http
   member 10.10.10.254:http
}

Note that snat automap will use the self IP address assigned to the created vlan, whereas creating a snatpool and assigning the same IP address as your virtual gives you a certain level of control.