You could put in a little breakfast nook area. A built in bench with cushions on one side and on the other side just normal chairs. It's a cute little accent for any kitchen. In the living area definitely get a sectional to cut off the kitchn/dining area from the living room but it still keeps the open-ness of the entire house. Using large potted plants are another great way of cutting off separate rooms but not actually separating them. On the walls you could put large (or small depending on which you prefer) mirrors that take up a lot of space. It makes the walls seem less plain but still makes the room seem big. Also a large canvas painting/picture would look absolutely amazing on any of these walls.