Rabbit cut:
So that is what that kind of cut is called.
I recently made a juke box, where I cut a 2 X 4 like that to use as a base. The juke set down inside the cut in the 2 X4s.
I used my table saw and had to make two cuts on each board. I called them "L shaped cuts", now I know the real term to use.
looks like a great job you got started. I like that cherry ply too, but it may be a little too expensive for me, except maybe for a small bartop or juke?