1. Many will say yes. I say negligible. But, insulate your roof regardless. Reflectix glued between headliner and metal roof makes a world of difference.
2. I'd say about 50 if you aren't heavily loaded. Your ride will be positively punishing if you run the recommended 80 or whatever it is on those, my BFG KO2's (E rated) were 80.
Okay cool. For the time being(4 kids/daily driver) we have no plans to build out the interior. So it will stay stock with just the rear captains and one bench seat. My tire guy put them at 35. But the light is still on. I will be pulling a 5,000 lb camper this weekend. I will run them up to 50 and check the ride.