[Kusuri]

1) no
2) no
3) no. there aren't that often new jailbreaks, so you don't need to really pay attention to that TOOOO often. so just jailbreak & disable automatic updates, done. you don't really need updates from amazon & often they make changes you don't really want (completly overhaul of the UI, patching of jailbreak exploits etc), so i would just disable them. if you rly need a update because a huge issue, you can update manually anyway.


but to make it short: jailbreaking does change zero in the terms of battery drain or anything else (well, the non-jailbreak apps atleast. KoReader etc. are different apps, so they use different battery amounts). everything works exactly like before, but better since you have more possibilitys. i jailbreaked my kindle the second day i got it, and it was the best decision in my life.