As Maq said, silica sand is not soluble, it will not contribute to any silicate levels. The Amazon river system runs over very well worn sand, almost pure silica. The water has been running through the terrain there for thousands of years, washing almost everything soluble away. The silica sand is still there 😁
The matter of hydrogen sulfide pockets is a topic that could easily need its own thread, but the general view here on the forum is that there is a lot of warnings and fear, and not quite as much evidence. Its possible that this could be a problem in some setups, but from what I have seen and experienced so far in around 20 years of fishkeeping, it seems that the problem may be somewhat overstated. I have used sand all these years and have not had a problem like this. Currently I am using very fine sand, 0,1-0,5 mm grains. I dont experience any smelly pockets or problems with plants rooting. You are unlikely to experience a lot of sand getting into your filters and equipment, I only saw notable amounts of sand when I was keeping this very fine grain sand and also had large whiptail catfish. The sand only ended up at the bottom of the canister filters, none of it made it to the impellers. Properly washed sand will be the least messy substrate for a tank that frequently sees plants uprooted, the dutch masters use sand for a reason. So in that case the soil will cause the most silt/disturbance. Your other points are totally fair and I dont want it to seem like I am trying to sell you on sand, I really am not and I think it is best for your plans and preferences to stick to your original plan of soil. I just had to clarify a few things 😁
I hope you dont take mine and Maq's comments the wrong way, we just love a good discussion, we cant resist 😉 I could tell that you already have a lot of research & knowledge behind you, and I think its very good that you know what you want and dont want. If you ask 5 aquarists their opinion I bet you will get at least 6 different answers, so knowing what you want helps to navigate what can be a really confusing start for most. Im still pretty confused tbh and sometimes feel like the more I learn the less I know 😅
Ill be quick to say that specific lighting units isnt my area of expertise (although im very passionate about uhh... sand, plants and certain families of fish😅 ), so this one might be best answered by someone else.
But my initial impression is that 9 hours is a little longer photoperiod, you might be a-ok with this but the super standard advice is to start out somewhere between 6-8 hours. Another super standard safest advice is to limit ramp up and down to 30 minutes each, but again this is a guideline rather than an absolute fact. The longer you have the ramping the greater the odds are that something unintentional is going to enjoy your periods of low light (so possibly algae). Your intensity doesnt sound too bad, but you should take into account that depth of tank plays a factor in how much light gets to the plants.
Silica sand wont give your water any more silicates. Theres sadly a bit of misinformation still going around the hobby about this, including from generally ok sources like Green Aqua.
We have several threads on this on the forum if you dont mind a search, I found one of Darrel's
latest posts about this, you might be able to follow the links back to the other thread.
Dont get this if you are planning to get corydoras or similar bottom dwellers. Black diamond blasting sand looks downright nasty under magnification. I know some people insist that its fine, but for me the close up pictures say enough.