Yeah, most cases act as kind of an insulator which is one of the reasons to just kinda turn it off if it’s in the case and you’re traveling, but otherwise not. Luckily it is pretty durable and won’t just sweat itself to death immediately.

Yes. I usually leave whatever game I’m playing on, running, on sleep mode. It’s always fine. I do however, make sure that the fan is not blocked off, and that it’s plugged in so I don’t wake up to a dead deck. Otherwise, there isn’t any danger that I’ve noticed- everything runs fine. If you’re NOT running anything and put it in sleep mode, any percentage above 15% should be fine. Turning it on and off actually takes more energy than sleeping it does, so I’d just keep doing what you’re doing.