I like the usage of lower keys as trigger - Some thinking-out-loud ideas...
7) Start Stop a metronome and adjust its speed (follow the rythm)
Switch on/off/dim my LED lights above the sheet music.
9) Send a signal to my PC to switch to the next page of sheet music e.g. page-forward in a PDF; another key to start at the first page again. A far more complex application could include selection of PDF's etc. No need for PC keyboard/mouse, Midi driven application
10) Make a PC MP3 player MIDI controllable, for play along with some music - practice .. some similarity with 9,
11) Start my coffee machine !