rhysoul nailed it on his suggestions. If a dealer ever tells you that you need to replace with only Kia parts to keep warranty valid, according to Federal law The Magnuson-Moss Warranty Act makes it illegal for companies to void a warranty or deny coverage under the warranty because an aftermarket or recycled part was used. If they do tell you this, they are required by law to give you said part for free.“Just say no”
Just have what you brought it in for done.
Cabin and engine air filter you can easily do yourself for $25 and plugs are simple and shouldn’t be more than $50 for the plugs.
Fuel induction service is something some people like to do because of our dirty GDI engines, but to be honest it’s probably more of a waste of money.
Brake flush might not be a bad idea given the age of the car, but an independent shop can probably do it for less.
Doing your own maintenance won’t void any warranty. Just save the receipts.
Regarding brake flush, buy a cheap turkey baster syringe. This works for power steering fluid as well. Put open end of baster in reservoir and pump bulb end of baster to extract fluid (brake or p/s fluid) until no more fluid in reservoir. Fill to line with fresh new brake or p/s fluid. You won't get any of the old fluid out of lines to brakes and p/s pump but removes much of the dirt in the system. Less contaminated. Good luck!