I tinted mine 5 days after purchase in Jan. lol
As far as percentages go, I got 20% in frnt and back because I don't like the look of two different tints on the side of the car. BUT in retrospect 20% in front is a bit too dark for clear visability when making left hand turns on dark roads. I find myself rolling the window down a bit. Check and see if your shop has a 30%, you can do a 30/35 or 30 all around.
Florida law I believe is 28%.