as the golf has 3 way component speakers you have a choice from focal, then hertz, jl, rainbow, a/d/s, morel
subwoofers u have a good range from alpine, jl, orion, fi btl, pioneer, etc. ive got 2 alpine type r's
amps good ones genesis, jl, orion, zapco, etc.
any 4 guage wiring will do copper one are best
a good agu fuse 90amp or above
power caps are not needed thou they help even the voltage out from spikes. i have one in mine a vibe 1.5 farad as my lights dimm when thelow bass drops still didnt help
even with as bigger battery looks like i need the big 3.
anymore info u need just ask ill try and help