It's a rockin' panel for sure... but I did similar by just buying an X-Keys programmable keyboard!
http://www.x-keys.com/xkeys.php
Great quality, easily programmable, very reliable (mine now about 11 years old, and has been reprogrammed over and over for various duties - now probably about to go into SAC duties after seeing your setup. Probably not as much fun as building and programming up as your own Arduino project though.
You can even buy a 'stick' version that fits into a rack-mountable adaptor...
http://www.x-keys.com/xkeys/xkstick.php
I have no connection with X-keys, other than as a happy camper.
Sonovox.