depends what type of tunes ur gonna whack in, u going for a bass monster spl system? or a high quality sweet sounding one?
Either way id recommend a little more sound proofing in the old golf, some dynamat in the boot and some in the headlining(bizarre but effective)
Give us all more of an idea of the type of install ur going for and im sure peeps will all give u some ideas... my system comprises of:-
Alpine 7838R head unit
Alpine V12 F407 4 channel amp
Alpine DDrive 6x9s
Rockford Fosgate 6.5" components in the front doors
12" Longmill cyclops in the boot
Rocky Fosgate wiring throughout
its cost me about ?700 for it all...sounds pretty good too, although id like to replace the sub with a better one and add a monoblock amp 2 drive it so the 6x9s dont run off the head unit..
Cheers
Ows