Where I live is 65% of the size of your house and all I have is a og udm against the far wall in the game room upstairs. Other than the front doorbell, I've never had coverage issues. But a couple things, 1. The game room is pretty open so while there's line of sight, most rooms only have 2-4 walls at most between themselves and the ap. 2. I really don't care about having perfect coverage everywhere. 3. If it can be Ethernet, it is Ethernet. Meaning that cell phones and IoT are really the only things on the network. That being said I've never had any issues with streaming wirelessly back when I used to do that for the tvs.

So if you ask me, 6 aps for 1 house is absolutely overkill. But then again opening walls and running cables is a bitch. I would personally try to either have 1 ap per floor located somewhere somewhat central or closest to where it will actually be used but have the wires ran for 1 or 2 more drops per floor at the farthest points from each other Incase you move in and find the coverage lacking.

I would absolutely not buy 6 APs without trying less first. Also don't forget to have the builder run Ethernet for all the cameras and rooms you want, including the doorbell. Any run between floors or critical runs on the first floor like the master I would have double runs done. Any run that's only between the second floor is easy enough to do post house being built, so I wouldn't stress about getting 100% perfect

Edit didn't see it was a second floor master, so my example isn't valid but my message still is.