This is a set of terrible—strangely overly-generic and overly-specific: use any DB, the DB was specified; use memcached, why? how?; CGI::Application? Hacka', please—recommendations that look as though you did not read the OP.

Reminds me of the best advice I ever got in my professional career. I pass it along for other readers. My supervisor at Amazon said: Answer the question that was asked, not the question you wish had been asked.

Of course, if you would like to provide a little code, perhaps you could show me where I'm wrong or misunderstanding your advice.

Nothing in the OP particularly suggests anything that calls for a higher-level framework like Catalyst or Dancer ... CGI::Application and its brethren just might be good enough. Expressed concerns about the number of rows in the database-tables being queried are irrelevant so long as the queries and table-indexes are properly designed. Expressed concerns about the number of sessions are much the same – it will not matter. (Portions of requirements like this one can also be handled using tools like RPC::Any if the decision is made to do most of the presentation client-side using JavaScript.) Frameworks can be very helpful but they also introduce complexity which might not be necessary in an apparently-specialized internal use case like this one seems to be.

CGI::Application is essentially CGI done with proper dispatch and slightly better abstraction but not all that clear to a beginner and easy to abuse and make a dog's breakfast. CGI would be the least complex here so it seems to be your real recommendation. No one should be recommending either today. It's like suggesting a hammer and box of nails over a nailgun. It might look a little less complicated but you are doing the seeker of advice a disservice. And I don't believe it is easier or necessarily less complicated than Mojo or Dancer. I think it takes a lack of familiarity with the packages to make your assertions. They were specifically designed to make web work easier. But maybe I'm wrong. Show us some code to demonstrate your point and I'll capitulate.

Come to think of it I can only remember one monk who recommended RPC:: stuff by route here. Always also without code or sense. But the handwaving show was worth the price of entry. Say... you haven't met that monk, have you? Likes to say things like, "all you have to do is design it perfectly and it's easy," "here's a tool from 20 years ago that will come in handy in case you are going to do something unrelated to your question," or "you asked for A but nothing you wrote particularly suggests you are asking for A."