I live in a vintage condo in Chicago. There are hardwood floors in the bedrooms. Refininshing them is not an option because they are laced with plywood. Obviously repair work. I live above another unit, so there is noise. I plan to lay 5/16" engineered. My questions.

1) 1/4" cork good for noise reduction?
2) staple or glue?
3) Can I use an inexpensive electric nailer or stapler to shoot 1 1/4" brads or 9/16" staples? Will it hold through the cork? I need to do in stages and don't want to rent over the course of a few days.
4) An other advice?
5) Am I crazy??

Thanks much!

Glue the cork down and glue the 5/16" down to the cork. Or choose a floating floor with Quiet Step or similar. Forget the nailing idea with those products. And you would really drive your downstairs neighbor crazy if your nailing above him.