Coming to Mac from the PC Master Race and building my own rigs, I would rather void the warranty and perform a iMac DIY teardown for repairs and upgrades than use Apple's costly and time consuming authorized dealer.
I understand the sentiment, but it doesn't cost much, and this machine doesn't differ from at least the last 5 years of iMacs. I took my 2013 27" in to my local shop with a Samsung SSD and the necessary ram to max it out and got it back for 50 or 60 bucks. Everything works perfectly and now my machine is maxed out.