you need geogrid on the first layer above grade. + the layers your propose.
you should go with 2 full blocks of embedment. 6" embedment isnt great on 72" height. 12" is stellar.
i would use 3.0/300 grid. but then 150 is biaxial and faster.
you cant charge a homeowner 5 grand for engineering, they would never go for it. commercial jobs only do it due to liability, even then sometimes they test for compaction sometimes they dont...