Whats your budget?
As far as your speakers go, if CF says 6-3/4" all around that sounds like what you'll have to use.
But if your stock speakers aren't blown and sound okay... Then don't replace them
They will literally sound atleast 2x better with just a new deck.
As far as decks are concerned i've been a fan of pioneer as far as adjusting the EQ goes and user friendliness.
Remember to turn HP filter on deck to 80 or 125.
Dont buy from crutchfield unless you want to overpay for crap.
http://reaudio.com/specs.html#sp_sxxRE makes great quality for the money.
But srsly...
If your stock speakers aren't blown... and if you have fronts and rears... then keep them until they do blow.
There is no way, once you adjust your new deck. that the stocks won't be loud enough.
Srsly.. throw on a new deck and you can get 2 fifteens with an aftermarket alternator and push 2500 watts and you still won't blur out the sound with the bass...
It may be fuzzy but definitely still audible (and thats a lot of fucking bass man).
Also.. the kicker L series aren't bad. Still kinda pricy though.
I had 2 L5's for 4 years in my daily driver with a zx 750.1 amp
Remember that there is nothing wrong with underpowering by a couple hundred watts. It's actually preferred if you want your shit to last.
And even with my subs being underpowered by around 200 watts. (1000W is as high as you can pull on stock alternator, i was doing a 750 which tested out around 790 watts... kicker underrates their stuff) i wasn't missing out on too much bump.
Cuz going from 750 watts to 1000 is only gonna get you around 1 or so decibels ... big whoop.
Hope some of this helps.