I am not a professional but I am in the middle of doing similar things to update my kitchen. I think your kitchen looks nice and is not at all hopeless. I would definitely add a backsplash. Consider honing the granite so you get a matte finish instead of polished. I would consider updating the pendant lights there are plenty of nice one on Houzz pictures. Subway tile and barstools are good idea. I would keep them in neutral colors.

very nice. some stools w/wood and metal or with a color you like, would go great.)

you have the perfect kitchen to do a little pattern w/the splash. doesn't have to be flashy. something along these lines would really give more visual interest than plain old white subway tile. your granite is dark and solid, so you can have something different for your splash. (no cool grays for the colors. )

a little color wouldn't hurt, these greenish crazed tiles would look nice w/the black and the reddish tone of the flooring