Some more ideas of things you can do with midi/gervill with sfxs:
* doppler shift with pitch bend
* positioning with balance
* attenuation with volume
* environment effects with chorus, reverb and lp filter freq/bandwidth
If you have a channel for each sound source and manage/prioritize these depending on context, it should be a pretty straightforward coding adventure
Gervill has also an implementation of key-based tuning, which you can use (see the demos). It also has a bunch of different chorus and reverb filters that you can change with some fancy midi messages.