Is there a practical limit to the number of files and folders on an AFP volume? I am interested in having some AFP server (such as a UNIX computer) with many gigabytes of storage, but would like all of the files to appear to users as a single file system. Would AFP limit how deep or wide the catalog tree could be in this type of situation?

The maximum number of files for a volume has to do with the maximum number of files that the HFS volume or Mac OS Extended format (also known as HFS+) volume supports, and has nothing to do with the AFP version since AFP is based on the HFS or Mac OS Extended format architecture.

Thus, the maximum number of files for a HFS volume is still 65,536 (2's 16 power) due to the limitation of HFS volume (4 GB), and the maximum number of files for a Mac OS Extended format volume is 4 billion (2's 32 power) due to the maximum volume size of 2 TB supported by the Mac OS Extended format architecture and the Macintosh ROM. Note that the "real" maximum number of files also depend on the number of blocks created and the size of the drive.

Important: For users running the Mac OS older than version 7.5 and using a Macintosh as an AFP client, the maximum volume size must not exceed 2 Gigabytes (the maximum volume size supported by the Mac OS older than 7.5). For System Software 7.5.1 users, the maximum volume size has been increased to 4 gigabytes. Software 7.5.2 users can address volumes up to 2 terabytes but there is no supported AppleShare solution to serve volumes of that size.

Note : Under AppleShare client software older than version 3.5, the maximum volume size the AppleShare client software will support is a few hundred thousand bytes less than 2 gigabytes (2,147,483,648 bytes). Apparently there was a small bug in the AppleShare client software that caused it to have problems when accessing volumes that are 2GB in size. This problem was fixed with the release of Macintosh System Software 7.5 which includes AppleShare client software version 3.5.

Something else to consider, it typically is not very efficient to use multi-gigabyte storage devices without using partitions to cut down on the size of the volumes in use.