You will still need to run a FCD,If you are seriuos of doing this swap,dont wait to buy it all at once..

Buy items here and there,or when ever you find it.
Start off with,
the rear end...
drive shaft...
Clutch,
Fuel pump...
afc/ or standalone

One question I got it,alot of S5 dont come with 4 piston calipers in the front,does your?If you dont know how to identify them,single pistion calipers wont say Mazda on the outside of them.4 piston will