You're lucky to see them drink. A couple of mine also like a good drink after eating.
When they're dehydrated, their skin appears wrinkly and their eyes get sunken in. With a ready supply of drinking water, this is very rare in captivity.
Their temperature depends on where they've been spending their time. If they've been at the cool end then they'll feel cool and if they've been at the warm end they'll be warm. The variation is fine and it just means that they've been thermoregulating as they ought to. It's all good!