Honestly, when my 2018 needed new tires - at 50K miles, I purchased them on tirerack.com. Got a set of Pirelli Scoprion Verde Tires and had them installed a local shop (they ship directly to shop). The total price was less than $1000. And the best part is that the tires were 100X better. Quieter, more traction, very slight drop in gas mileage but nothing major. Liked the process so much, I replaced the tires on two other cars the same way.
I would also say that on my 2018 CX-9, the only thing I ever did was change the oil and replace the tires. Loved my CX-9. I also very rarely ever used 93 octane. For me, 87 was fine.