Up to 35 real servers. If your environment is bigger than that, or you expect to grow past it soon, the ADC 440 supports 50 and the ADC 540 supports 100, so there's room to move up without changing how you manage your traffic rules.

Yes. Direct Server Return is a Barracuda load balancing mode that sends incoming requests through the ADC 340 but lets responses go straight back to the client instead of routing back through the appliance. That keeps high-bandwidth responses, like video or large file downloads, from bottlenecking at the load balancer.

Yes. Content rules let you route requests using the URL, domain, cookies, or HTTP headers from the incoming request, so different types of traffic can go to different server pools instead of every request getting treated the same way.

Both. Alongside load balancing, it includes built-in intrusion prevention, access control lists, and protection against the OWASP Top 10, including SQL injection and cross-site scripting, so it's stopping attacks before they reach your application servers, not just spreading traffic across them.

You can deploy two units in an active/passive high availability cluster, so if the primary fails, the second takes over without dropping traffic. It's a common setup for anyone who can't afford downtime on production applications.