For V5R4, the maximum number of objects that can be associated with one journal is 10,000,000.
The maximum that can listed at one time in the STRJRNPF command is 50. As Phil said, run the command again to add more files to the same journal.
There is no limit to the number of files that can be journalled, but there maybe a limit on a specific command.
Just use STRJRNPF as many times as you need to.