I'm ignorant about the complexity of those rules but I would consider balancing/redirecting all anonymous users to one exclusive server, maybe except for the login page.

Like this logged in users and especially admins could work and improve the site.

And the bot logs would be available on the other box.

We also need a dev/test server where we can patch the core Everything:: modules, probably a second installation on the less busy hardware could do, accessible under a dedicated sub domain. Cloning the modules and libraries should do to get this running.

High performance caching is certainly feasible, but we need to implement the triggers to disable a dependent cached page on update events. And I think we need better benchmarking than just server logs to evaluate the best strategies.