You are correct no oil additive is needed. I also switched to Motorcraft full synthetic 5w30 at my first oil change. With that I'm going with 5,000 mile intervals. I would presume a Ford dealer will use the correct Motorcraft oil filter.
I had 19x9.5 +33 wheels with 275/40 all around on an S550 for awhile. Lowered on BMR springs. No rubbing. On my S650 I currently have 275/40 all around on 19x10 +35. Lowered on Steeda magneride springs. No issues.
My S550 developed that at about 55k miles. It was noticeable at above 40 mph or so. It turned out there were metal shavings in the diff fluid and new gears were needed. Fortunately it was covered by the powertrain warranty.
You shouldn't be having an issue like that with a new car. I would...
When I installed BMR minimum drop springs on my S550 the rear shocks were hitting the bump stops because I didn't trim them enough. Not sure what you mean by "bottom out" but replacing the bump stops solved the issue for me.
I live in DFW and I'm gradually seeing more and more gen 7s but still see a lot more gen 6. I definitely see a lot more Mustangs of all gens than Camaros. Chargers and Challengers are plentiful.
It's probably in quiet mode the whole time. Those first 30 seconds are likely even louder when you cold start it in normal mode. These cars are very loud on cold starts.
Now that I have an H pipe, cold starts are noticeably louder in quiet mode than they were when the exhaust was stock. Cold starts in normal mode are much louder, though, which means quiet mode still "works."