yeah that sounds about right. I had 10mm in my mind. 12mm would be better actually. 19x10 +13 would give you a slight poke to match the rear. I'm running a x10 +20 and I'm flush, so I think the +13 would complement the rear, cuz that rear is really aggressive
I'm running P Zero Nero's. They have rounded sidewalls. You're going to need to find a rounded sidewall for that rear.
I still think you should make the front more aggressive to match the rear. Rear's gonna poke, and front is not quite flush. What look are you going for?
I used to run stretch on my benz and liked the Toyo T1R's as tires. Check em out