Hello New Delhi!

1. I don't know the answer to that, these stones may be too big if anything. They would help aeration, but by the time you get enough of them, you might be substituting too much of the soil.

2. I would think so.

3. Yes. It should provide some ventilation underneath.

I think having some shade over the pots themselves and the ground underneath would help with the heat issue. You might go over to the Container Gardening forum and search for posts about 'heat'.

@toxcrusadr thank you. I did post the question on container gardening forum a week ago but got no response there.

Yes, definitely. At least crushed pumice. Crushed pumice would serve the same purpose as perlite in potting mix. It doesn't retain water, but it creates space for both air and water. In fact, most container gardeners use perlite rather than pumice because perlite is cheaper. Maybe pumice is cheaper for you.

On the one hand, perlite is less dense than pumice, so creates more space, but because it is less dense, it more easily floats, which is not an advantage in keeping a mix well mixed.

I assume your floor is hot because the sun is shining on it. The sun will shine on the pumice too so I'm not sure you have a lot to gain. But sure, pumice stones would be good insulators.

2 and 3 are yes!

To prevent the pots from heating up as much, put the pot with the plant into a larger pot (pale colored, not metal) and leave the air space as insulation. By preventing sun from striking the pot you keep it a bit cooler. The outer sleeve or "cachepot" should be 2-6 inches wider than the inner pot where the plant is.
Keeping the pots elevated off the pavement helps

Putting all the potted plants in a group helps because they can shade each other.

Thank you all, much appreciated.