before doing any monitoring, load testing or tuning, you need to setup a detail model, a goal, even it's hypothetic.
I had help a customer develop a site host 17,000 users using weblogic6.1, it's a data entry type application, we basically gone thru all turning possibilities on network, weblogic(cluster) and database. It's months of work. But I am afraid you won't get any specific answer as the way you post the question. You need to explain the natural of your app, your reqruiement on throughput and response time. memory estimation for invidual user or transaction etc. If you have not done the ground work, do it first.