Just an observation, the clamp you are using to secure your ATO level gauges will rust big time if you continue to use it. Then when you go to remove it later some rust may fall into your sump. Might want to find another way to secure it

Anything that is around salt water should be really corrosion resistant (metal and wood) or you'll wind up with problems.
I like the direction you are going on your tank. Looks good.
My 2 cents is go for the cheap LEDs. Two would be better than one on a 48" tank. I have two cheap Bridgelux lights and am growing SPS so they definitely are powerful enough on my 75G tank. The only thing I would do is have the vendor customize them to get some lower nanometer LEDs in your array. The standard is 455nm and 10K white and I found I needed to add back an old PC actinic to really get some of the fluorescence and pop that I had under my T5s. Next LED I buy will have some 420nm and maybe a UV or two.
Good luck!