Spoiler for How many cubes...

should be in a tray to prevent the tray above it from ruining the cubes below?

Assuming 4, then I would make 1 tray of cubes and then use it to make 3 trays with 4 cubes each and fill those with water with another tray with only water on top.

This will then give us 36 cubes. Again I put in 24 cubes in 6 trays to prop them all up and one tray of water on top.

This gives me 60 cubes in this cycle. Rinse and repeat for 60 cubes in each cycle...

Assuming 4, then I would make 1 tray of cubes and then use it to make 3 trays with 4 cubes each and fill those with water with another tray with only water on top.

This will then give us 36 cubes. Again I put in 24 cubes in 6 trays to prop them all up and one tray of water on top.

This gives me 60 cubes in this cycle. Rinse and repeat for 60 cubes in each cycle...