I can't answer your questions definitively, either, but I can offer a caution about who to ask. What works in soil work -- compaction, excavation, fill layers, backfill etc -- is very local in nature. Methods that work well in south Florida are NOT appropriate for Southern California . . . and vice versa.

I would *strongly* encourage to talk to LOCAL contractors, pool owners, and / or inspectors, and weigh that advice heavily against any information you gain here.