I think the back 1x4 will eventually bow to the weight of your lights. Three or four pounds will place a significant stress on the corner and thus the long board that you're using for evelation. Perhaps if the back piece was turned 90 degrees to increase the strength of the support, then attached to another board perpendicularly to making mounting it to the stand more effective... JMO of course.

I think you would have a cleaner, more professional look, if you use aluminum bars? Or if you wanted to you could mount to the ceiling and use panduit to run the power cords to the lights. Panduit is the same as conduit only it runs on the surface of the wall rather than in it. Simple to use, just attach the flat piece on the wall where the cables will run, then snap the tubed portion on top. You can paint to match the color of your wall/ceiling.