How to echo to multiple midi channels ?

Hi and welcome!
 
You can create multiple midi tracks all set to the same midi input, then set the output of midi each track to it's desired channel using the dropdown menu (located either at the bottom of the inspector for each track or to the right of the track name area if you expand the view). Activate input echo on all of the midi tracks, then whatever you play will be sent to all of the channels you set.
 
For more advanced mapping, there is a brilliant program called Bome Midi Translator that will allow you to do most anything, but I don't think you need it for what you are doing here.
 
Good luck!