There are stable cm builds available. At least 4.1.2 jelly bean. There are 4.2.1 jelly bean roms, but they're less stable. I get better battery life with custom roms than I so with stock. Every custom ROM gets better battery life for me, better performance too. But your millage may vary. I think it's super easy to root and since you have rooting experience it shouldn't be a challenge.
All you basically do is: unlock bootloader, flash twrp recovery, flash new ROM. There are much more detailed guides available here. With the latest update I think you have 2 options to get s-off: Facepalm and DirtyRacun. Both are pretty much automated I believe. Emphasis on pretty much.
I don't have much experience with the latest OTA, but if you need help with rooting I or one of the many other helpful people can help.