Bash with AppleScript could be stored as a part of you FileMaker script or as data in FileMaker fields. This will allow every user to use them and no danger to erase them. I would definitely use this route, unless you get PC users in the mix
You can not delete a folder from FIleMaker natively. If you already have a full list of files in the target folder you can delete files one at a time, as this is something FileMaker can do.
You other option is to use plugins, local or server-side.
All I had to do was Google "Applescript create folder" and "Applescript delete folder", copy the script I found, and paste it into the bottom panel of the Native Applescript panel of the Perform Applescript step.