When reading this the only limits that came to mind are the file size, WinMX has a limit of 2gig for files. It wont share a file larger then that. As far as opennap limits those are set by the server owners and will vary with each one.
You may also hear there are limits to the amount of files you can share and this is not so, there are however limits to the amount of files a user can browse. So if im on secondary I can only see 3000 files in a browse, and on primary i can see 5000. All your files you share above these numbers will however be visible on searches.
Hope this helps its the only limits I can think of at this time..and not sure if they are mentioned a lot in the other tutorials..