Sorry the images didn't get uploaded, I will add them here

I would tile the walls around the outside of the alcove to the bottom of the cabinets, but inside the alcove just tile the bottom flat area to the window, or put a solid piece of your countertop in the alcove bottom. I don't think you need to tile the sides of the alcove.

No tile on the flat please. Sill that matches the top with returned ends.

Tile the platform of the window well only.

I would tile across under the window only only.

Update:
So we have remaining counter top material to use in the window sill. Down side is that it's 2 equal sized pieces, and hich 1/2 inch short. CAN this work? How to fill the gals at the edges

It looks like you have a small front overhang on that peice. If you made that peice flush with the tile, would you have enough to trim from the back to use as filler on one side? If that can't work, I'd just center the peice in the window and put some sort of filler on each side.