All a3's parts ar swappable .. from 2013- 2017 should 18 too but must be 5 door all round and 3 door only front end is same rear end is different cannot mix with 5 door
about splitter you won't find it for non- sline .. bumper better of to upgrade to sline/s3 bumper and buy splitter for that ..
remember pre-facelift splitters are different fitment to facelift so u need to look for 2013 to early-2016 splitter or facelift late 2016- early 2019
In your case 2013 u need to get pre-facelift sline bumper first then buy splitter for it or you can buy facelift bumper and buy splitter for it
but that's not good idea as you would have to buy new facelift headlights too haha