Pool filter sand looks like about 1-3 mm particle size. Play sand is generally much finer, too fine for a planted tank, in my opinion, but I know some people use it successfully. Flourite is larger particles, but Flourite sand is about the same as pool filter sand, or a bit finer.
Please don't take this wrong but, I was kind of expecting something a little more "creative" as a solution to mounting those lights. I remember a few thousand posts ago you showed us a DIY articulated arm you built. I was very impressed with that one.
If I see your name on DIY, I go there 1st. So, tell me do you have a pro to-type on the drawing board on on the work bench?