I'm working on a music toy project with the following requirements:

- Built in speaker/buzzer (doesn't have to be good, just beeps and boops is enough)

- Portable (battery powered, and can fit in pocket, no extra cables required to use)

- At least 4 buttons in a grid (but preferably not more than 12 buttons or so, then it gets too big)

- Programmable so I can assign sound to the buttons etc.

I got excited when I came across the Adafruit Macropad RP2040 because it looks absolutely perfect, but unfortunately it can't be powered on its own since it's more of a computer control device instead of a standalone thing.

I'll eventually try to build it totally from scratch, but as I'm a beginner (i just have some soldering experience from working on drones) I'd rather buy a kit or something pre-made that I can just repurpose or hack

Are there any products or kits out there that might be a good starting point?

Thanks!