I've spliced everything that needs power off of the cigarette lighter power wire. I never use the cig. lighter, and I know first hand that it can handle having 11 different things spliced and powered off of it
I think there's a ground for the stereo you can splice into, or you can bolt down a ground wire to a section of metal frame that sits behind the stereo.
Did you want the lights on the gauges to dim with the other interior lights? I still haven't figured that out, but I like being able to dim the dash lights and have just the gauges blazing bright.