How to raise Backyard Chickens: [CHICKENS-101] Bunch of Broody Hen Questions

Hey there,
I have the three broody hens, each sitting on fertilized eggs. They are due to hatch mid-June. I have a bunch of questions:

The coop is 2-1/2 feet off the ground with a 1/4" mesh base. There's a lot of Orchard grass in the coop but the hens have been digging their nests down quite a ways. It's been in the 80s days and 50s at night, I'm a little concerned about the eggs getting chilled from the bottom. I have some old roofing shingle sheets that I was thinking of sliding under the hay and over the mesh...good idea? bad idea?

I know that it's a good idea to candle the eggs. When, ideally, does this take place?

There have been a few broken eggs, and some small pieces of the shell from have gotten stuck on the whole eggs. Hopefully this will not impede the chick from hatching. I didn't want to remove them for too long from the hen. or to use water to clean them, so I did what I could to chip off the shell pieces, anything else i should have done?

One of the hens was off the nest for awhile, I'm not sure how long. The eggs were cool to the touch. She's a Cochin and not really good at jumping up into the coop under normal conditions. I foolishly removed the step to clean and forgot to put it back. It could have been up any time up to maybe five hours on an 85 degree day. I lifted her up, put her inside and she settled back down on the eggs. Could the eggs be okay or should I assume the worst?

The Brahma was initially in a box that I think was too small for her to get in and out of easily. She was pooping in the nest. I removed her from the box, took the eggs out, got rid of the box, built a nest in the Orchard Grass and and she seems much happier. However I've noticed that her vent and the feathers around it are just gross. Is there a way I can clean her off or should I just let it be for now? She doesn't like me messing with her.

Last question, I promise ;) the three hens are in a semi-divided cage. One hen is on one side, and two are on the other. I've been trying not to mess with the hens too much, but I'm assuming that the each hen and her hatching eggs would need to be separated, before the eggs hatch, correct? And that each hen raising her chicks will need their own space as well? I've read that Mama hens will be aggressive toward other Mama hens. Has anyone had this experience and if so, how did you solve it?

Thanks in advance.
Worried Chicken lady