I haven't touched the throttle body or mass airflow sensor on my elantra GT. However i have changed the spark plugs on a previous car and it was pretty easy. most spark plugs will come pre gapped now so you might not have to worry about that but if you do a gap wrench is pretty easy to get. you should be able to take the ignition coils off the engine and underneath those is where the spark plugs are. im including a image with the ignition coil's circled in red, its on a 2011, but it looks close enough to my 2013's engine bay. the spark plugs can vary, almost nay will fit really and you can find a set of 4 performance copper tip plugs on CARID for somewhere below $15. the only real thing to watch out for is making sure that they aren't too tight. make sure to use the seize lubricant on them so they don't get stuck. and make sure what ever you use to tighten them in place doesn't drop them in there because if they end up falling in and getting stuck its too much of a hassle for you to fix that scenario. as for the gap, i think Stock the gap is .44, you should be able to do all of it with a socket wrench, two different sized bits and a extension or two. If ( i learned from experience) you turn the car on after wards and it sounds like its having a misfire ( believe me you'll know, its loud and bad) you may have just gapped them wrong or one of the ignition coils may not be on firmly.