Alpine are always the way to go with headunits, they've always had the best signal to noise ratio... Depends if you listen to cd's or mp3's as to what headunit to go for, although personally I still stick with cd's for sound quality, but that's just me, if you want to save money, you can get a second hand headunit off ebay that sounds the tits and costs bugger all eg cda 9811, cda 9812, 9815 etc that will have three preouts, very good sound quality etc...

You should buy the kit yourself even if you get someone else to install it as you will save loads...

JL Hertz and Rainbow are all good brands, always recommend the XR series JL as my mate had it in his competition (winning) install I helped him with.

Sound deadening you realy should do yourself, it really isn't hard to change doorcards, remove rear quarters etc (guides on forum)...

Edead is cheap but you have to use twice as much, Dynamat is still the best option...

And you would still benefit from a sub, even if you just go for an 8 inch in the boot as the front speakers can be low passed so that they are not overworked on the low notes and the sub can fill in the missing notes that you would otherwise not hear/feel. Also JL do a good 8 inch sub that would match the fronts, they even do a 6 inch sub if you really don't want much bass or have issues with boot space...

Spending £100 on sound deadening will benefit you more than an extra £300 on speakers (honestly). Even if you just do the inner door skins behind the speakers you'll be surprised just how much difference it makes... Also the cable to connect the amp to your front speakers is one of the most important things NOT to scrimp on, you will notice the difference if you don't get a decent triple shielded one...

For the setup you want and the budget you have, you don't need the rear speakers...

Hope that helps a bit, have done dozens of installs (although my car is currently devoid of ICE as still sound deadening it)... lol