Hello,
What happened if we not set the tx power? Will the AP operate with maximum power?

It will operate with the maximum allowed power in accordance with country regulations and selected frequency.

Hello,

What happen if country not set?

It will work, but you must be careful because you could start transmitting with greater power than allowed in your country and if you have strict regulations about transmit power you could get fine if they caught you.

Hello,

What happen if country not set?

If there is no country set...it is automaticaly USA

If there is no country set...it is automaticaly USA

Maybe in those devices sold for the US market. Otherwise, no.