I believe that will work well, because--as I understand it--the MP5 is supposed to send MIDI events for most keyboard functions (some older keyboards would make functions like new bank selections work only internally and never send the MIDI events out). I'd recommend opening the MIDI I/O window of Organteq and press a few of the MIDI event buttonsyou want to program on the MP5, if it shows up in the list as a MIDI event, you're ready to go, otherwise, you'll need to tweak either the keyboard or Organteq settings. Once you've confirmed that Organteq is getting the MIDI events it needs, then you should be able to right click on any feature or icon and select MIDI settings for that stop, piston, pedal, etc. and have Organteq attach that feature to the MIDI event you trigger.
Spotify:
https://open.spotify.com/artist/2xHiPcCsm29R12HX4eXd4JPianoteq Studio & Organteq
Casio GP300 & Custom organ console