Use node count as a test plan, not a coverage promise
Square footage cannot describe masonry, metal, mirrors, long wings, floor construction, or an edge-located internet entry point. Start with the estimated count, place the first router openly and centrally when possible, then measure the important rooms before adding hardware.
Device count describes load, not wall penetration
A busy network can justify more capable hardware, but a premium router does not send a useful signal through every obstacle. Separate capacity problems from coverage problems by testing near the router and again in the weak room.
Prefer a strong backhaul over an extra weak node
A wireless satellite needs a usable upstream signal. Place it between the router and the weak area rather than inside the dead zone, or use Ethernet backhaul when practical. One well-connected node can outperform two satellites repeating a poor link.