For reference, I have a 22 GT2 AWD that I've had for almost 2 years and about 36,000 miles. I drive a good mix of city, stop/go traffic, and highway road trips.
1) I haven't had any issues with the carbon build up and I don't worry about it too much. I think some people are overly cautious about it and install oil catch cans and use treatments. I've also ready posts from people who have high miles, never did any preventative work, and haven't had an issue.
2) At my last oil change the tires still had good tread left on the original, stock tires ( Michelin Primacy Tour A/S). There was more wear on the rears than the fronts, but that's to be expected and the difference wasn't drastic. The tires have a 45,000 mile manufacture warranty (half that on the rears due to the staggered setup per Michelin) so I've been happy with my wear so far. Obvious, "your mileage may vary" depending on driving style. I'll be looking to replace them in the next 6 months or so. Also, I live in Minnesota and haven't had any issues with the stock tires in the snow.
3) I honestly haven't had any high cost maintenance done (knock on wood). I've had zero problems with the car since I bought it in 2021, and I've just followed the maintenance schedule. The dealership by me is no BS, they haven't tried to upsell me or get me to do useless work. A very, very minor annoyance is that the oil needs to be changed every 6,000 miles (3,000 under extreme circumstances such as winter weather, but I've still only changed the oil every 6,000). My last car (a 2018 Accord) would go almost 10,000 between oil changes. I totally understand the difference between the Stinger's
3.3TT engine and the Accord's 2.0T, but at my current mileage it's been about twice the oil changes.
The only unknown high-cost factor to consider is insurance. Insurance is such a hard thing to compare, but my insurance more than doubled when I bought my Stinger. Nothing on my record, no at-fault insurance claims, nothing to really be able to pin it on other than the car itself.