Hi Ashmita,
There is not a restriction about the number of directory paths, but you should consider your scenario and to restrict a the number of directories if you have a large o medium files in order to avoid the system overlaoad.
Check this wiki http://wiki.sdn.sap.com/wiki/display/XI/Optimum+File+Size+for+various+file+scenarios+in+PI+7.0 and this thread http://scn.sap.com/thread/1531187.
Regards.