client authentication means the CSS will request the client to send its own certificate and we will check its validity with the configured CA and configured CRL.
It has nothing to do with the CSS certificate.
So, you could have a self signed certificate on the CSS. That doesn't change anything for client authentication.
The same IP thing is probably not a good thing if you want to assign the certificate to different domain.
A dns request will only return an ip address and no port.
So you may end up with all requests going to the same ip and port 443.
I think the limit is 256 ssl-proxy server.
Check config guide for assistance :
http://www.cisco.com/en/US/docs/app_ntwk_services/data_center_app_services/css11500series/v7.50/configuration/ssl/guide/terminat.html#wp999318
Gilles.