I am currently doing these items on mine. The wishbones (for a V6) last around 20K as it's a heavier lump, so the twinny will get more life out of these items.
With regards to the front, do shocks and springs at the same time as its a false economy not to. Go for either KYB or Suplex Springs with either Alfa OE Shocks / or KYB (I have found Osram and Magnetti Marelli one's for the V6 at under £80.00 each) - I believe these are cheaper on the twinny.
Also, replace the Drop Links for both ends of the car, as that will make a big difference to the handling - plus if there is any excessive play here its an instant MOT fail.
Rear setup: Poly Bushing is a must here for both the Spring Pans and Dog Legs. Again for Springs, use KYB or Suplex standard springs with either TRW or KYB Rear Shocks.
Euro Car Parts have up to 50% off at the moment and you can get the rear shocks and front drop links from them no problem. With regards to the remaining parts, there is plenty on Ebay. (i.e. KYB and Suplex sellers).
With regards to Lower Wishbones - if they were done years ago in your service history, then do them at the same time. Alfa Workshop has good prices on these items and go for the TRW one's which are the same as OE (as made by TRW) but cheaper than the OE one's as they don't say Alfa Romeo, but who cares tbh!!
Alfa Romeo GTV Wishbones front
Don't go for cheap Ebay one's as its a false economy!!
Once you have done all this, don't forget to undertake a proper 4 wheel alignment (not your crappy Kwik Fit Laser Line Hangers) as they only do the front toe. These cars are 4 wheel adjustable. Will set you back around £70-£100 depending where you go etc.