1.Since you are in Europe, i suggest that you conctact either (www.pure-pf.com
) or (www.ca-at.co.uk
( phone # 0871 231 1010)), iam sure both companies carry Turbo manifolds rated at over 500hp.
2.Uprated disks and pads should be enough for the street,even if you want to track the car, there are pads will give you enough stoping power and pads life on the track.
3.The stock head gasket should be good for anything less than 9psi, but if you are planning to go big boost then you will need that stronger part.
Edit: Also i believe that stock injectors will not be able to supply the sufficient amount of fuel on 8psi of boost.