still new and learning....... what parts from a s5 are better than the s4 parts. i know the turbo, but what else? the rear tailights are a looks thing, but what parts are actually "better" thanks

 

I'll tell you one part on a S4 that is better than the S5. its the little junction piece that is directly above the turbo that feeds into the intercooler, but also has 2 other smaller ports going to EGI or emissions junk. on the s5, its plastic, and after so many heat cycles it cracks or breaks open completly. on the s4, its metal. the stuff that doesn't crack open like an egg when exposed to heat.
besides that, i can't think of much you could swap over that would benefit you. just save up for a big turbo, fuel pump, injectors, bigger intercooler and a haltech and make big power

if you don't have the 4pot brake calipers up front, you could find some of those for cheap

 

Rotors (higher compression), turbo, VDI (on n/a), and my personal preferences the shifter/**** and stereo console. The shifter seems to have a shorter throw than an S4 and I find less destroyed stereo consoles in S5's than S4's. It's easy to swap over into your car if time has taken it's toll. Took me about 30 mins on a Saturday morning.