35% is for pussies. get 20% all 'round. Just make sure your windows are rolled down when you get pulled over.
AAP is correct also. You can spray paint your back windows black if you want, but front passenger compartment windows are supposed to be no darker than 35%. If you went 35% on the front, 20% on the rest it wouldn't look bad.
As for mobile tinting...you really want it done in a clean environment bro. Any speck of dirt gets magnified under tint. Some guy in your driveway, with wind blowing debris around...nah. Go with a reputable place too. You spent $$ on your car, why go cheap on tint?
As for the ghetto factor...maybe my boy Puddles just wants to help protect his investment. Sun and heat can wreak havoc on a car's interior. I know, I know...his geighborhood only gets sun like 50 days a year, and only half of those are hot, but when you're wearing shorts and hopping into a leather seat on a 90 degree day...you'll be thankful for those tinted windows!