Where would you start your adventure with building FPV drones having a background in electronics/CS?

I thought about buying kits/parts from Aliexpress, reading books (not that many are available on the topics), or starting with some Udemy/YouTube courses but I am not sure if those are good starting points.

The goal is to fully understand the principles, structure, and mechanics (electronics and firmware) of those drones for fun but also to build a proper skillset.

I guess this may be an interesting topic for many of us here.

Please share your stories, ideas, and sources.