Want to get multiple years out of my 2015 Subaru Crosstrek - Premium (Current - 60000 miles) but am not sure how much if at all of the Subaru suggested 60k service is necessary. I can change the air/engine filters myself, but would need help with spark plugs etc. Should I follow the service schedule? If so should I go to the dealer or my regular mechanic if it's still under warranty?
Service schedule is a guide that's there to follow. Where to bring it to have the work done that's a different story. Car still under warranty doesn't have any bearing on scheduled maintenance and wear items, you still pay $$ for any services you want done, and dealer service dept. will usually try to upsell for things you don't need.
https://www.youtube.com/watch?v=i2jrzcARors
Using your own mechanic is fine, but you do want to do all of the recommended services in order to get the maximum life out of your vehicle.
First of all, do not go to the dealer because most people over there don't know how to do simple stuff. Change the spark plugs for 60,000 miles first time. And then change it every 30,000 miles after that. Don't take my own word for it yet. I might be wrong. So others like @Mod_Man can help you with that. I just researched online.
Change your transmission fluid, drain+fill
Yes follow your owners manual, but for the transmission fluid don't believe the 100k mile interval or "life-long" sealed non-sense change it every 40k miles or so, if you haven't done it yet definitely get that done. Oil change every 5k... Other stuff refer to the owners manual maintenance section