you don't need specifically the G60 induction kit, I used to always have it over a G40 one for future expandibility, also liked the noise, lol.
You can just use the G40 one, slightly cheaper... I think the G40 one is actually 'flow rated' for 400bhp so Id think it'd be enough, lol.
If you were after saving money, don't have the cam just yet. The stock G40 is very good.
Exhaust doesn't have to be Stainless, I used to have a mild steel custom made system, lighter for the track car and cheaper (cost me £220) though last you about 2-3years. If you need to decat, then you'll need a non de cat downpipe from VAG (it was £90 years back), or cut it off the stock G40 one and get a sleeve welded over with boss welded too for lambda.