Should My Leopard Gecko Tank Be Warm Leopard Gecko Substrate?

Leopard Gecko Substrate? - should my leopard gecko tank be warm

I will be one or two female leopard geckos in a tank to take thirty liters. I have all the orders right, and hygrometer, heating pads, light, hide box, and hideboxes wet. In just not sure on the substrate. I do not use sand, but retains heat really welll. I read somewhere that you deposited a layer of sand and is covered with a large piece of the plate. Sand and the tile would be perfect for hot and leopard geckos. Is this true or a good idea? What else is there to the substrate (more sand). How many female leopard geckos, I should for my thirty-liter tank to get? Thank you, I will choose a best answer.