I don't know if it'd be wise to put a bead of adhesive down. It wouldn't necessarily be unwise, tho. Mainly, it won't matter one way or the other, until it comes to time to remove the decking, should you ever decide to do that. Adhesive just adds one more thing you gotta deal with, before and after. The screws will hold the plywood deck down just fine without the adhesive, and if for some reason the screws don't hold because of a moron forklift operator, adhesive won't help.
As for how many, see the other thread.