Help me build a musical telephone

Community charity project for the elderly. Based on a concept well-described on Github, need an "electrical" builder who is able to build a musical phone. It is essentially an old Singapore rotary telephone, which upon dialing a number will play a song. Outcome is to have a simple PCB in a small case where you plug the phone in, so the rotary phone remains intact. It should work with the Arduino Pro Micro, a simple MP3 player, optocoupler some capacitors and resistors to tie it all together. For a video of what I'm after, please go to: https://www.youtube.com/watch?v=6hEOnSAb5wg. It's in Dutch, but you'll get the concept. In addition to building it, I would also like to document the process for SG rotary telephones so I can get builders in Singapore excited about this and start building it for their aging parents / grandparents also.