This is shaping up to be a great build. It looks like you solved the overlap problem on the sides. I'm always impressed when someone creates their own return edges, and your work is no less impressive.
I think your belt will cover the notch area anyway. You may be able to trim a tad off the abdomen plate, but you are correct in that it will be better to trim most off of the kidney.
I'm always having issues with excess glue. Sometimes you can use a pencil eraser to remove it after it cures. Then you just have to buff out the eraser streaks.