I LOVE the house! So pretty! I definitely think painting that inset wall in the living room is a good idea!
That tall wall in your living room could honestly stay bare. I think it's ok to have bare walls sometimes when you have a house as big as yours. In the office, you could do a big calendar or sort of corkboard/chalkboard on the big wall. In one of the hallways near the living room/backs up to the kitchen, you could do a cute string of square photos on. I do love gallery walls, because I love pictures of my family, but how many gallery walls is too many? Who knows! I also love a gallery wall of empty frames or vintage mirrors.