Web Server consolidation fronted by Wildcard Cert design question....

So I would create a separate pool for each URL(54 pools). Associate all of these pools to one VIP and put all 20 servers in each of the 54 pools?

The above is just one example. So let's say you have 54 applications running on one physical web server, listening on different ports. You'd create a separate pool for each application, then use the iRule to direct traffic to the right pool based on Host header. You technically don't have to have a pool assigned to the VIP assuming the data group will match every URL request. If you installed those same 54 applications on another physical host, then you could add those instances to the individual application pools and load balance them. This stuff can all be scripted by the way. If you had 54 applications running on a single physical web server, listening on different IP addresses, the approach would be the same. How you implement this ultimately depends on how you've provisioned those 54 applications on the 20 servers.