Hi
If security is not an important issue to your network, choose mesh without security. This is a usual choose.
When creating your own application, you should chande only the application layer of one of the existing Beekit codebases which seems closest to your own application.
If you load your modified code to a zigbee node that was defined as a Router in Beekit configuration, it can be used for extending the range of the network.
Hope this helps