I am slowly running out of IO on my Arduino Nano. The code for the Arduino Mega AR3 looks exactly the same as the Nano AR4 code apart from a ton more i/o obviously.
Are they directly compatible? Any reason not to go with the mega?
I was also thinking of switching to a Pi Pico W and do all my GPIO via Wifi or bluetooth...
Yes you can use the Mega code, I just switched to the nano on the AR4 because it was lower cost, took up less space and has more readily available terminal breakout boards.