"I have to define 6 WAN interfaces. Any other way?"
Huh??? You would normally just put the vips on the interface actually connected. I don't even think pfsense will let you bring up another interface in the same network?? So at a complete lost to what you have done.
If you have been given say 1.2.3.0/29 where gateway is 1.2.3.1 and you can use .2 -.6 You would say give pfsense the .2, then create VIPs on this interface for your .3, .4, etc. You would then forward your traffic that hits your different vips.. Ie if dest is 1.2.3.6 port 80 forward to 192.168.1.100:80, if hit .5 then 192.168.1.99:80, etc.
You can name optX anything you want. If you gave it a gateway on the interface then it would auto think its a "wan" interface and allow for natting to this interface, etc. This is how you bring up different wan connections when you have different ISPs etc.
But again I am like 99.99% sure pfsense will not let you create another interface and put an IP on it that overlaps another interfaces network.. So what you have done I have no idea.