The power will plug straight in but you'll need to swap over the perm live & ignition on as Audi wire them back to front.
You'll need an antenna amp for the aerial as Audi HU's have an amp built in.
If you have a changer then sell it as it won't work.
The sub and rear speakers are powered by a seperate amp inside the sub. The feed to it uses a non standard mini ISO connector, so if you want to connect this up you'll need an adapter. If you're running your own sub then best not to connect it up as it's pathetic and the sub will just fart & distort anyway. Also the rears will be underpowered in comparison to the fronts. Instead just run new speaker cable to the rear of the car from the new HU's rear speaker outs and either splice it into the red plug on the sub to pick up the rears or connect it directly to the rear speakers by pulling off the rear speaker panels.
You'll also need a fascia adapter to fill the gaps on the oversized Chorus HU. Audi make everything so simple!