Re: Flooring layout
I just put down 3/4" mats, no ply. The only weights i drop are bumper plates, no damage to my concrete floor (I oly lift near the front edge so I've lifted the mats to have a look.) I don't think you're likely to damage your concrete floor unless you're dropping your 2 pood kettlebell from overhead or dropping steel plates....but then you'll also be wrecking your oly bars as well.
The mats do shrink when it's cold, last year I just had a squat stand with nothing anchored through the mats so when they shrank, I just kicked them tight and away I went. Now I have an R6 bolted to the floor and the mats cut out around the feet of the power rack so the mats stayed in place and there is a small gap (maybe 1/16") between the mats. I'm not super hung up on it, it'll warm up in a few weeks and the gap hill be gone.
If you like overkill (and who doesn't) you could probably just throw down the ply without bolting the mats to it and you'll be happy as a clam with your results.