I once tried drilling through a chunk of that asbestos sheet siding. That stuff just glowed and made sparks. Used a spritzer bottle and a few squirts of water ant that hole saw bit sunk right through.
Dug another ~8 cubic meters = 8000 cubic liters ~10 cubic yards~280 cubic pounds soil.
This time there will be 20mm~3/4 inch plywood formwork ($50 4'x8')
I do not know what kind of permanent staircase will be, straight, with a turn or spiral. it is necessary that the hatch in the floor is about 1x0.8m (~3'x3') - no more.
Thats nice. Can two or three buckets be linked together ? Winch sound like it has enough power to lift that much of a load.
Just thinking outloud is all.