i have used the jaycar amps a few times and they have been very good and even better value. a cheap option for an amp that is great bang for your buck is a brand called cutting edge not sure if they are still round.
as for a sub i am a fan of the 10 or 12w3v2 from jl audio for mild to mid set ups but again you should choose the sub that sounds best for the type of music you listen to.
what ever sub you get it should be in a box that is the correct size etc etc.
as for the install you might want something like in the last post here http://www.skylinesaustralia.com/forums/in...opic=106866&hl=
mr 32