The more light output, the more “juice” it takes to get that output (and the runtime suffers). The more juice flowing through the head of the light the more heat produced. So yes, all lights with significant output will get hot. You can’t get something for nothing. I’m sure other folks push their lights far more than I do, but I only use turbo for when I need it and then sparingly. The electronics are in the head and I don’t feel good about heat stressing the chips. The heat produced is the reason some lights will ramp down the output; to protect the light from damage. There are only a few ways to get rid of the heat produced that I can think of. Use it in a cold environment, or increase the mass, that includes adding water to the head as in a diving light or using it in a rainstorm, of course increasing the mass also could mean adding more aluminum to the head and handle and adding more fins to transfer more heat to the air. Yes the handle will conduct heat from the head of the light and warm up the cells also. In theory the cells could get so hot that they break down but I don’t know if that has ever happened in the real world. The batteries do have protection to help protect against that, but others will need to jump in here to give you more info’ regarding that. I use only quality cells for the safety aspect. Never use inexpensive cells that make fantastic claims about capacity. Basically if you read about cells being used in these pages you can sure that they’re quality. But even then you can get into trouble by using cells in dangerous ways.
You can read about cell safety and such here: LEDs & Other Stuff - (Reference Guide)
It’s an absolutely huge document, but cursor way down in it and you’ll find a few areas regarding cell safety and what can happen and such.
Sorry, that’s all I have for you. I can’t answer your other questions.