I ended up installing 3 units M9 for my house (2 floors, not quite sure about size... probably 120sqm) and it does the job very well. I would expect 2 units to be enough... or you are unlucky :-(

@rg_village Thank you for this very interesting question and thanks for all answers.

@Solla-topee I was hoping I could just connect one of the TL-WPA.... items and it would communicate with the TL-PA... Is it not the case? If not, could I just not put any wifi router at the end of...

I bought a powerline set TP-Link TL-PA7017P (french sockets) I would like to provide wifi capability at the end of this "network". Could you suggest products that would do this, please? I am not...

Is it possible (or even reasonable) to try to connect an old TP-Link TL-PA211 to an AV600 adapter? So far, it looks like the answer is "No"...