Best Orbi system for large area

With WiFi everything depends on placement and building materials.If each floor was a 24 meter square open space and the access point is located in the exact center, then one access point would provide excellent coverage of the entire space.  Shape, interior wall construction and placing the access point away from the center might result in poor coverage in some areas.  For example, if the building is more "long and narrow" and the access point cannot be placed in the center, the area farthest away (with the most interior walls between) might not get adequate coverage.  This is the case in my house, where the ISP connection is in one corner of the 2nd floor. (1st floor in Europe).  The entire house is only 2,100 sq. ft., but coverage downstairs in the far corner was pathetic. (about 230 sq. meters), so I added a satellite downstairs.

The Orbi product line does not have any "outdoor rated" satellites compatible with the 960 product.  What many people do is place a regular satellite inside a plastic weatherproof utility box.  There are obvious issues with providing electrical power and backhaul signal to an outdoor location.

Other Netgear products do have outdoor rated satellites.  They often use Power over Ethernet (PoE) to provide both power and data signal to the satellite.  (Low voltage cable can be passed through walls, whereas "mains" voltage cables cannot.