Lights I can't say much on... I swapped all of the interior lights to LEDs, so nothing fancy there.
Speaker recommendations... The best I can say is go to a store and just listen to them. I have used Polk Audio, Kenwood, Pioneer, Kicker and Infinity over the years in various cars. I like Polk Audio and Kenwood for interior speakers. I have never bought an expensive set of Focals or any other $800 set and I most likely never will, so I can't give an opinion on "high end speakers". You can snag Polk components and 6x9s on eBay for $100 each. Add another $100 if you want to do something with the rear doors.
Back to head units... There are so many choices out there. I guess you need to decide what you want out of it and how much phone integration you want. Do you want iPod control, satellite, HD radio, back up cam, rear DVD? Navigation units are overpriced in my opinion. I guess the sky is the limit as is your pockets. The only issue I have with Pioneer is that you have to buy one from an authorized reseller or they will not honor their warranty. That is on their fine print on their website. Don't know if Kenwood or others do the same thing.
