The last time I tried to program the ATTiny85 to be controlled by midi, I did not have a lot of luck. First thing is that apparently you need to have a bit of precision on you clock. Internal clock speeds for these chips have low precision.
Also, midi is a standard…but a loose one at best it seems. There are lots of ways to send the same note. The midi controller I had did not send things like I expected it to. And yet it was compliant to the spec. Still, this is hopeful.