Question 1: I plan to seal the niche wall gasket with silicone, is this okay? ( I understand the inside niche and junction box connections will use a special potting compound).
Q. 2: I will need a niche inspection, which will include the niche conduit, (with a bonding wire inside and out, potting compound, etc.). I would rather run the elec pvc higher, just below the bonding grid, but that would mean covering the niche with backfill, and therefore the outside bonding lug connection. Does an inspector need to see the niche outside bonding connection or just the inside?
Q 3: Is about a 5' pigtail of #8 bare copper sufficient for the niche to the equipotential grid?
Q 4: What elevation do you see commonly see for elec pvc runs under the decking?
Looping the elec down to the plumbing would make for too many 90 deg angles.
Running the elec pvc higher would mean backfilling all the way up the walls, covering the niches.