If you'd really prefer a clip light, you could also get a piece of plexiglass at HD and cut it yourself (if you score it you can snap it in a straight line for the overall size and then dremel out the openings for everything) Might be safer than glass if you're cutting it yourself. (I'm assuming you are trying to save $ otherwise i'd just suggest just buying a glass canopy)
I think the layout looks good, but of course it's hard to tell without seeing it in action
Also, you could return the filter and pick up an azoo palm
or red sea nano filter
(as far as I can tell they are exactly the same thing with different brand names stamped on them). I've found that filter to be perfect for a 5g planted Betta tank, and it's only 2-3 inches deep, so you should certainly get your 1/2 inch back!
You clearly know a lot more about physics than I do, but it would make me nervous having any tank hanging off an edge even a little bit.
OR you COULD keep the filter you have and hang it off the side, but then you'd definitely need to do some finagling and make yourself a glass (or plexi) canopy. I did that on my old 20g tank, it was in a hallway so I wanted it right up against the wall, that made the only option hanging the filter off the side and it worked just fine.