If you want to be running on the latest Jelly Bean Android 4.1.2 and have a ton of customizations over stock Jelly Bean, check out AOKP Jelly Bean ROM for your Kindle Fire. I think this is certainly the best ROM out right now for your Kindle Fire.
AOKP brings a ton of UI customizations to your Kindle Fire while also giving you a pure Google experience. You can customize many things including the lockscreen, power menu, sound, add weather/calendar widgets to lockscreen, and much more.
Beyond just that, if you want to turn your Kindle Fire into a pure Android tablet devi