I started with things as they are in the documentation, then I tried with one per page request and that still gave me performance issues.
One per session might be ok, but I would start with just a single bucket per application (which is the way I am trying now).
As I understand it the SDK should manage its own connection pool internally, if you find you have lots of simultaneous requests you may want to adjust the connection pool properties on the bucket settings within the web.config.
See also Using Couchbase Buckets pattern