I think all white with the center part of the ceiling painted the wall color (with the medallion white) would highlight it best. The potential problem with this is the back wall. Did you consider putting a thin version of the curved arch along the back wall to complete the rectangle? Breaking up the horizontals and verticals will be chopped up, imo.

Can you post a clearer plan with legible measurements and the exact location of the beam? You are more likely to get good help that way. From what I think you are describing it sounds like the easiest option would be to eliminate the last wall cabinet, if that is the one affected by the beam. You could substitute some open shelves below the beam instead. Something like this:

The window trim change would be to Craftsman style. Unless you are doing the work yourself it seems a lot of expense for little difference on upstairs windows. It would, however, be extremely easy to do on your front door as you would only need to change the top board. And you could replace the side lights with solid wood inserts, or you could use textured glass that would obscure the view while still letting light in. While the limestone exterior is very light it has a yellow hue. Simply speaking the easiest way to find colors that work with the warm limestone is to choose a nearby color. That was probably why the trim is green. Since you prefer a modern look, I suggest you keep your siding light and use color only in the trim. Below are two combinations that I like. I darkened the roof color in these pictures.

https://www.houzz.com/discussions/5870468/we-need-help-soffit-and-trim-color