Given a new, clean slate, everything necessary to function would be on a single level with no steps from the garage or outside into the living quarters, and as suggested, every passageway at the least 36" wide. Remember that around an island in the kitchen if you have one, too. The laundry would be near the bedrooms instead of near the kitchen. People generate much more laundry in the bedroom/bathroom than in the kitchen; carry the dishtowels to the laundry room and back, not the shirts/shorts/socks/towels/pants/etc.