I'm about to start a similar project and although there no guarantee it will be finished any time soon, I will bookmark this topic so I can add a link when I have completed the necessary information gathering...
The project relates to building a basic midi keyboard (61 keys or so), generating on/off, velocity and possibly aftertouch data... Note, I won't use a diode matrix for keyboard scanning, probably something more on the lines of a common bus (polled configuration)... Anyway, I thought I mention it in case you loose interest...
I still have to determine what is necessary to use uno in midi mode, believe I need to reprogram 16u2 and a few other bits and pieces...
Mike