I would never build under 1.25 KS either. That is the dimension where you can still sit at the head of the bed when the headboard is under the slope. Anything less restricts too much, even in the children's room or bathroom. I would rather do without the bay window. It is so unnecessary. Instead, you can put a dormer on the upper floor. The costs may be about the same: bay window vs higher KS. There should be a storage room under the stairs. Keep in mind that no proper clothes/wardrobe cabinet can fit in the hallway by the stairs. The niche is not deep enough for that. I find the children's rooms excessively large. Instead, there should be another storage room upstairs. Where are sports equipment, towels, seasonal clothing, suitcases, and such going to go?