I'd suggest small amplifier, mono, or stereo,
then you can work out connection methods, power supply.
TBA820M (small 8-pin DIL IC, 50 cents)
together with 100K potentiometer.
it can be powered from 5V (USB), and still is reasonably audible.
when you have more experience you can build real amplifier.
same for microcontroller: start with the basic models, which do not require complicate configuration. you can save a lot of time. later when you understand how they work, you can spend efforts on the configuration.
it is no shame to make a coloring activity from a monochrome blueprint, and neither it is a shame to build a simple IC based amplifier.
as long as power supply, connectors etc. are made nicely.