You’ve been working hard. This is fantastic!
I would agree with Osik about the position. Bottom left is better. This is where most players put the art.
I have produced another mockup. Notice I have extended the playlist area to fill the gap.
I need to think a little more about the “no cover” issue. Most players either display a blank CD or some text. I think I prefer text as a CD is not very representative. We could also use the text to explain why the cover is missing (e.g. get your tags sorted out!). I will go away for a bit and think.
How about this for no cover.