Hey Chirp, nice setup!
I can help on some of your questions.
Placement: everything looks pretty good, nice schematic btw, I would place the Bubble higher up and not between rocks, put it were it won't abrade anything with its polyps. They are quite delicate. Shrooms
are lower light and could go on the fringes of your light coverage too. A nice hammer or frogspawn would be nice in ? Area, as long as it can't reach your brain, and they can extend tentacles about 5 inches, to attack. They would be OK by the torch, you don't WANT them touching, but they are about evenly matched, and will co-exist.
Supplements: with weekly pwc
's, with a quality reef salt, you don't need to.
Marine snow is actually a coral food, not a chemical supplement. Feeding corals is dependent on the amount of light available, and the type of corals. Most corals don't really NEED food, except non-photosynthetics, with adequate lighting, but many people do feed. As long as your system can handle feedings and export the waste efficiently, IMO
it does help.
Lighting: sorry don't know much about the LED
's, I run T5's, but many people are doing well with them, post a thread asking about LED
's specifically, and someone will help.
Hope this helps, looks like a good plan, and good luck!