Great write up, and nice Onitukas!
I'm planning something similar, already got my LEDs from onzium. But I also want them to come on with the fob, door unlock etc.. I'm hoping to piggyback on the interior dome circuit for that, using diodes so I don't bridge circuits. This of course requires the dome circuit to be positively switched. I HOPE HOPE HOPE it's not negatively switched. But I'm not sure, since I haven't put a multimeter on it yet.
Any clue if our dome is negatively switched?