ISPs outbound load balancing

Hi I have with some specific request and doubt, I am instaling a solution with DNS and LTM to make a outbound load balancing of ISPs. My architecture is

 

Selfip1 x.x.x.2 selfip2 y.y.y.2 selfip3 z.z.z.3

 

Node1 x.x.x.1 Node2 y.y.y.1 Node 3 z.z.z.1

 

Pool_gw with 3 nodes default route with pool_gw

 

I can see that the load balancing is working, but in the guide I can see that I make a wildcard VS, but is not clear for me, which type of VS(standar, forwarding IP, performance Layer 2); I try whit 3 and only work with forwarding IP, but in this virtual server I can specify any pool; please your help.

 

Another question I have a specific requeriment, they have 3 networks,

 

x.x.20.0 x.x.30.0 x.x.40.0

 

And they want that the net x.x.20.0 always go throught the isp 1 until this link is down; how can I make this possible, I try whit a specific virtual server forwarding IP but not work when I configure a snat_pool.

 

Regards