The way I switched tank to tub a few days back, is I held him for 2 hours until the heat mat had adjusted.
My UTH is directly on the plastic, and the plastic hasn't melted one bit.
I'm not really sure about that one.
Yeah. Adding more holes will reduce the humidity significantly because of more air flow.
My little guy doesn't have 2 identical hides and is just fine. But if you want 2 identical ones, those look good.