If the reports are all scheduled, the only problem with file-based events is if the timing of the event and the schedule get out of synch. For instance, if the process that creates the event file happens to complete before the scheduled time of a report, the report will not run; the event has to occur AFTER the report is scheduled to run. Of course, this can be remedied by renaming/deleting the file and renaming/creating it manually, giving the event server enough time to find the file gone before finding it present again.
If the users need to run the reports manually as well, they will either need to wait for the file event or you will need to write csp code to bypass the event requirement.
Another challenge is that event requirements cannot be set in ePortfolio; they have to be set in the CMC. And, if you have to change anything at the report level, it has to be done one report at a time. Crystal never made any provision for bulk changes to report-level (or user-level) attributes in Crystal Enterprise. I would hate to have to maintain over 100 reports; I think it would become a full-time job.