So, it seems that all what needed to be done is done.
On these pages you may find everything used for completing the project. Obviously I don't expect anyone copying the work, but I hope one day it might be of use to someone seeking inspiration.
I have unplugged my original drum module 2 months ago and have not had any regrets since.
Regarding future plans, I can forsee at least two.
1st - get rid of the PC and substitute it with RPi or another STM board.
2nd - find alternative to the cymbals, the one I have really bother me.