I can’t really speak to the difference between ESPs and nRFs - I haven’t played with ESP mesh networking enough to compare them. The nRFs just get used because I already have libraries that I use and enough chips on hand. (I would imagine the ESP at this point is superior in every regard? It just has such an ecosystem around it.)

For powering projects, it depends - most projects I do can be plugged into a laptop or into the wall - I have a programmable light array that is the main project I do with the kids. For other portable projects, I might use 18650s, might use coin cells, might just use AAs. This is a big topic and I’ve been meaning to write this up in detail.

Thanks for the questions! Sorry it took me until now to respond.