Thank you for your answer! You're totally right, auto pilot is not a so great idea (at least at this stage of the project), and a lot of things regarding security should be considered. It can become really dangerous if it is not under our control and something goes wrong.
The problem with onboard wifis is that there is often no way to put the adapter in "Monitor mode" and they don't support "packet injection" which is mandatory for wifi pentesting
Instead, I think I will use an Alfa 1000/2000mW adapter, it should be able to scan and penetrate wifis further away and supports it!
BananaPi M2 Zero was also on my list, but because of its poor support (no Armbian and the lack of information about its power consumption) I removed it...
Also, I haven't found any A64 board with a small form factor, but this would be a good alternative, sure!
And the PocketBeagle is the same as the BeagleBone Black right? The main issue, like the RPi Zero is its single core cpu, I have to make tests but I think a quad core cpu will perform much better for what we want to do!