Today I spent 2-1/2 hrs cutting and nailing in some more top and bottom wainscot trim and lining up where the vertical pieces will go. Most of the time was spent up in the workshop cutting out the other three bottom plates of the window boxes. You’ve only seen three windows so far but there is another window in an adjacent room that will receive similar trim work (but no wainscot).
The stairway is behind this wall (below) and you can see that the basement cold air return is an obstacle to trim around. I suppose there are a number of ways to deal with this; recess the grate, put a wide trim around the grate, or as I did, made it a flush fit.
I opted for a near flush fit for the vent screen.