Main floor gets a half bath, that's it. All bedrooms, full baths, and laundry upstairs. Downstairs is guest space, upstairs is family space.
I have to disagree, especially given the ages of the OPs. It is wise to think ahead and be prepared as we age. First floor should have at minimum one bedroom, or an office room with closet that could easily convert to being a bedroom... and one full bathroom (can be a smallish walk-in shower rather than a tub).
If you are building, you have the flexibility to build smart. One never knows when they may experience a mobility issue, especially as we age. It is easier to plan ahead than to have to remodel during what might be a difficult time. My parents' home had only a half bath and living/dining/kitchen spaces on the first floor, bedrooms and full bathrooms on second floor. Unfortunately, my father (who had always been very healthy and active) suffered a sudden, debilitating stroke. When he was eventually able to move back home, all bedroom furniture needed to be moved downstairs into the former living room (which had no door, so no privacy at all), and the half-bath needed to be remodeled to install a shower, because he cannot navigate stairs.
As for other things we like about our home and would recommend...
Tile or waterproof LVP throughout the ground floor is nice to have. You can use area rugs to soften rooms and to help define spaces within an open concept design. If there are spills or water damages for any reason, it is an easy clean up and no worries about replacing damaged flooring.
We absolutely love our large, covered, screened-in lanai. We spend a lot of time out there, for morning coffee, dining, reading, etc.. Prior owners even had a tv & sound system installed on the lanai.
Ceiling fan/light combinations in almost every room, including bedrooms. Even with a good HVAC system, there are times a ceiling fan is desirable to circulate the air.
Plenty of closet and storage spaces throughout the home. We really like having a pantry for food storage, along with hall closets, dedicated linen closets, and large closets (for clothing and storage) in each bedroom. If you will have a space under the stairs, also have this accessible designed for storage use -- don't allow any space to go to waste.
Separate HVAC systems and controls for each floor of the home. We have a second floor flat over the garage, where our adult son currently lives. He has his own HVAC system and controls for his living area, and we have our own separate HVAC and controls for the first floor. Makes life so much easier since we each can control the temps in our own living areas.
If you will have lawn irrigation, pay close attention to where lines are installed! Keep the lines closest to the home out from under the soffit/roof overhang. Speaking from experience. We bought an existing home and did not realize the line on the side facing neighbors' home was located under the soffit. Prior owner had also placed pop-up sprinkler heads on instead of stationary heads. Long story short... a pop-up head failed and the water shot up through the soffit and over the wall into the crawlspace causing ceiling collapses and major water damages to the tune of $35,000. All could have been avoided if the irrigation line had been located a few inches further from the house so as not to be under the roof overhang.
and then a huge rectangle (which use to be the walkable attic). I which the three bedrooms could be more square and more equal in size.
