I am doing my first engineering floor installation in the coming week. My house is on a slab. I installed laminate before in the room but now we want engineering wood. They are 7/16 thick square edge. Lauzon is the brand.
7 years ago, i had used self leveling compound to fix the concrete floor prior to installing the laminate floor. we are done with laminate and now we want hardwood.

i have a few questions before i start my project.

6mil plastic on top of the slab.
1 layer of plywood as underlayment - i want to use 3/8 thick as this match better with my tile floor in the hallway. Do you think this is ok or do i need to go thicker?

Staples installation over the plywood. I am not sure of what size staples to use on the engineering wood floor for the chosen plywood thickness. A recommendation of staple gun brand and model would be great.

any help is appreciated. TIA.

Two layers of half inch ply would be better. Then you could use a one inch long quarter inch crown staple with a Bostitch Floor Runner.