There is no absolute maximum number of requests the Enhydra multiserver can handle. The maximum number of requests depends on several factors including server memory, number of CPUs and application design. Enhydra's scaling method uses Enhydra Director to do load balancing.
Director runs as a plug-in to the Web server.
A single Web server can forward requests to any number of Multiserver instances. Heavy production sites scale by balancing requests across Web servers that, in turn, balance load across application servers. In terms of rough numbers, Lutris had run tests with millions of hits per hour over periods of days. Of course, your milleage will vary depending on a large number of factors. Enhydra Director allows you to do this.