Answer
There's no hard upper limit on the number of printers a single Print Agent can handle, but piling too many onto one instance can eventually strain it, so it's worth logically grouping printers (by location, department, function, or whatever makes sense for your organization) and running a separate Print Agent per group rather than one large monolithic Print Agent. Multiple Print Agents can run on the same server or on different servers, and connecting several Print Agents to the same IFS system is entirely supported — just make sure any individual printer is only ever mapped in one Print Agent, never duplicated across multiple. For geographically distributed sites, it's generally preferable to run a Print Agent physically close to each site's own printers to minimize network-related printing issues, though this isn't a strict requirement.