Hi,
we can use smart ADC devices from analog Devices for this project. it includes microcontroller with cortex m series. so, we don't need another external microcontroller, just add Bluetooth module.
and we can populate another circuit like your requirement. just message me over messenger and let's discuss the detail of this project.
I will use eagle / Kicad for this project. I have designed PCB since 2012 and has done lot of project for Hobbyist, Robotic, Industrial, IoT, and Military application.
I always following design vendor's guide when comes to critical application like ADC to achieve best performance.
Let me know your response, and let's finish this project together.
Best Regards,
Rijal