As long as you don't mind buckled up $hit in the middle of your floor, use all the laminate you want.
Yes plywood under the vinyl plank.
I find it funny how everyone wants to skip insulation due to lack of head room, then they waste 3/4 of a inch with useless plywood that could have been a sheet of steel 3/16th of a inch thick.
If you must use plywood, Jake C did it right.
http://www.skoolie.net/forums/f11/pr...utus-5059.html
Nat