Hi,
Sorry, I have no chance to try 5 or less users on my client site since it is festival period in my country, his business is very busy.
However, I have another client that use the same application with lesser users about 5-7 users, same hardware spec and also with huge amount of transaction per day without any problem of corruption.

BTW, i found that VFP table could be corrupted even just 1 user at a time. It happened while admin user try to "send update" of item info to workstation (one of customized module)

Even how, vfp table is really really easy to be corrupted. :((