We have done successful tests with about 300 files. We have just not tested more.
1. There are a couple of settings you should think of when testing:
a. check "Put Job in queue". This make VisualCron process one file at a time which prevents conflicts
2. use Variables to pickup the actual Triggered file.
Dynamic folder Variable: {TRIGGER(Active,LastTrigger,File.Result.Folder)}
Dynamic file name Variable: {TRIGGER(Active,LastTrigger,File.Result.Name)}
Dynamic file full path Variable: {TRIGGER(Active,LastTrigger,File.Result.FullPath)}
These Variables can be used wherever in VisualCron.
2. It uses Windows events. But you can choose to "poll" if you are monitoring a Samba folder or similar that does not support Windows events.