yes, you can do in ap mode, not in router mode.

yes. you can, but P7 need to be configurated first and M9 as sattelite

Yes. Just keep device priority order into your network M9 > P7 > M5 > M4 > M3.

yes, work fine on this way. Just use Fixed IP on NAS or assing fixed IP into Deco network. (Address Reservation).

Configure all decos before via wifi, afte this and network ready proceed this step: 1. Turn on 1st Deco, wait green light. 2. Wire and turn on Deco 2, if green light apear, Backhaul working. 3. Do...

For both questions, in AP MODE, the anwser is YES, Deco has support for this topology. In router mode you get red lights on Deco 2 and 3.