Pretty house! I would do them all the same for continuity.

I also suggest doing the windows all the same or it will look odd.

By grids are you talking about the mullions? i would vote to keep all the same but most mullions are removable. Try taking them out in the lowers (they should pop right out) and see how you like it.

Your style of house generally has a 6 over 6 window like you currently have. I would stay with that. If budget allows I would also put larger shutters up that are wide enough to cover the windows if closed. Yours are a bit too narrow.

Also, does your front door need to be replaced. If so please don't put in anything with oval leaded glass, etc. While attractive doors, they don't really enhance the style of your home. If the door is in good shape then just paint it. A bright red would look good with your siding.

I like the 6 over 1 look if you are replacing all the windows. Fresher appearance.