That's fun but I'm still missing some fundamentals I can't exactly put my finger on. Like: how to prevent microchip overload, how to stabilize a circuit, prevent rush-in current, handle different voltage levels, etc. I know how to drive a servo with an Arduino, but this still doesn't help me truly engineer a circuit.

Ah ok - well I was in the same place as you a few years ago and asked a very similar question here - and got interesting answers: https://news.ycombinator.com/item?id=16920476

5 years later I did not proceed with the electronics part. For one I did not have time but even now I realize that learning to properly do things in electronics requires serious studies. A typical problem I had was: how should I connect a loudspeaker (which resistor, capacitator, etc. to add and where). I found out that it is better to use "building blocks" that include all the electronics and require cabling and coding.

For instance, as we speak, I am connecting a NodeMCU to a relay module and all I need are cables and a 3D-printed case.

This is really a matter of personal taste though - I prefer to code than to design electronics gven that I have limited time.