Wifi design for new large house?

I know you're not needing a "real mesh" but I'd actually look at it. 

Something like the RBK43 version with a wired backhaul would have the same performance as the 50 series because the difference is in the backhaul. Plus it'd give you seamless roaming, the ability to add more satellites as needed, and even the option to use a wireless backhaul if you wanted. 

Plus if you look at it, netgears consumer line up of devices doesnt have an extender/AP that functions with mesh (same ssid capabilities) before moving into the business grade equipment which gets expensive. 

Not saying you have to but the single ssid function with seamless roaming works great in larger homes and is worth it. 

If you wanted a higher functioning router to control it all, you can do that and just run the orbi setup in access point mode. I've done that before with great success.