Sorry it took me awhile to get over here! I lived in a split foyer much like yours when I was in GA, so I know all about the challenges of painting. You could definitely, as suggested, put up a trim piece of molding on the wall where that 1/2 wall looks over to the foyer, to separate the paint colors in foyer & livingroom. That would work great for the separation. Trimwork and molding painted white.So, it looks like you were ALL right and we will be putting up a column/trim/something in the hallway to separate the colors. Yippee!! You learn something new everyday!
As far as the other parts, I actually painted one side of an overhang one color, stopped the color at the corner that turned down the hall and began another color that direction. So, when you were standing in my kitchen looking to the LR, the kitchen was one color, then once you walked to the LR, it was another, and the only separation was corner walls. It wasn't totally ideal, but it did work for me. So you might have some ideas on how to use that. I'm sure you will figure it out. Sometimes a corner can be a break in color, but make sure they flow!
I love the color in her blue bathroom, seen here. She blogged about the bathroom when she first painted it... awhile ago... and I sent a picture to Dear Husband. Maybe