I just wanted to let you know that I decided to give this a second take but removing more complex features, which ultimately required dealing with Android app development, which I'm not into.

Thus, I created BicycleCompanion MINI project, quite similar to this one but without Bluetooth and battery recharging (initially) and based on STM32F103. I plan to develop a custom PCB, which will allow for this device to be quite small.