Here’s a rough sketch of how I’m thinking the layout will go.

1/2 playwood will be secured directly to brackets at 16″ spacing. This should provide adequate support and prevent and sagging from occurring. At most, only 4″of plywood will overhang a bracket, so that shouldn’t pose a problem either.

Staging got dropped a lot, giving me about 7-9″ of clearance under the main level. I’m not sure how long the front valance will be either, but I drew it in as 12″. this would probably be secured using glue and “L” brackets attached to the underside of the mainlevel.