Received 5 x DFplayer mp3 boards today :)
Over the next few days I'm going to pick up for 512mb micro sd cards for them and then build my new breadboard up.
Code-wise for the screen and encoder nothing will change, but for the pad control I will need to initialize 4 software serial ports for the fkur boards, and the main loop will need to loop through the analog pins and send any read hits to that pad's dedicated player.
If it turns out that this is complete overkill i always just use two mp3 boards, queue the registered hits, poll the status of the mp3 boards and pass to the next available.
For testing purpose I'm going to connect all of the mp3 boards outputs together with 10k resistors, but in the final case I may include potentiometers to allow the user to mix pad strength.