http://www.bcae1.com
this site is very helpful, force yourself to read it several times.
as far as what 93sohc said, i think on most amps, you can turn down the power on the amp itself (at least on mine you can), so you may not have to get a 4-channel amp afterall... usually you can take a screwdriver and turn down the power on the amp (to the sub(s)) if you worry about your subs drowning out your 4 full-range speakers... but then again, most head units, regardless of what they claim to put out (ie 70 watts max power per channel), won't put out much more than 25 watts RMS (RMS is the way to measure the loudness of CONTINUOUS sound)
the answer for the first question---no, you dont NEED an amp for them, but it might be helpful so that you can get out of them their full potential... if you have really nice speakers that can handle a lot of power, its probably a good assumption that any head unit you'll buy will be "holding them back", meaning that it won't put out enough juice to the speakers to allow them to be as loud as they could be
for the 1000w amp question:
Max Watt Power is all crap... it's a way to confuse and deceive the buyer... always look for "RMS watts", "Nominal watts", or "Continuous watts"... that's what you really want to know about... oh, and yes, you will have to look for it on the box, because whatever big wattage number is plastered all over the thing in big lettering, that's the max wattage... so let's just say this... you have an amp that's 2-channel 500RMS watts @ 4 ohms(ohms is basically resistance, so the more ohms, the greater resistance to sound output)... i would then just look for 2 subs... they should be able to put out 250 RMS watts @ 4 ohms each.... that way, the 500 RMS watts available from the amp is evenly distributed between to subs which can each handle 250 RMS watts...
p.s. USUALLY, and i stress the word 'usually', max power wattage can be divided by 2 to get the RMS wattage... for example if an amp has 1000w max power, it's rms is probably somewhere around 500w RMS
p.p.s. but anyway, like i said, read that website thoroughly, and you'll know more about car stereo than you'd ever want to know, and it'll be of great value to you in the future, especially in determining what you want to purchase... do that, and keep on asking questions, cuz that's the best way to do it-pick people's brains who've been through it all already (you'll know what i mean when you're ready to take on the task of installing all of your equipment, cuz at that point, i'm sure another thousand questions will arise because of uncertainty and intimidation)
hope some of this helps