@DaveK Pretty much hit all of the major issues that popped up in my mind from your photos.
I would eliminate anything metal near your tank opening. Never use metal for any purpose that has any possibility of being wet. The lighting fixtures are dead wrong and I have to point this out. This is a fire hazard.
Another item to consider is the type of wood for construction of your canopy. Particle board has been known to release formaldehyde when heated. The only reason I know this is that I made the same choice years ago over a 29 gallon. It did not handle the water conditions well at all, and deteriorated quickly from "salt creep". Anything exposed to open salt water will eventually become exposed to salt. This salt permeates substances and then draws moisture toward it....which particle board readily wicks about.
What type of sand/rocks did you add?
I too keep a 40 gallon tank, and it is only a few months old. I managed a 4 tube t5-ho light fixture and bulbs for around $100. @ 36" long it is just over the edges, and I wish I had opted for the optional hanging mount bracket. You could get a dual tube light for even less.
There are endless possibilities for your tank, and they are at your discretion. From my experience, if you start out like I did I recommend keeping a "FOWLR" which is forum-speak for "Fish Only With Live Rock". This is a great place to start out keeping saltwater, as you concentrate on water params and learn to deal with the consequences of mistakes. Water quality that is used for tanks is paramount. If you mix your own salt water, start with RO water at the minimum. Most will advise RO/DI water.
Mistakes will happen. They happen to everyone that tells the truth, and even if they lie it was probably a minor thing like missed a top off of water. Do not ever let a few minor issues make you want to quit this hobby. The only reason tanks fail totally is because the owner gave up totally.
Wanting to get your feet wet is the first step toward a very educational hobby.