If you intend to run the mains off the head unit then look for very efficient speakers rather than a high-power head. Many companies way over-rate their stuff to make it look better. Peak power is only important if you listen to music with a wide dynamic range....this does not include most popular styles of music, but classical and movie soundtracks often have very dramatic dynamic changes and you'll hear the unit run out of power when it happens... at any rate. Go with Clarion, Alpine, or Eclipse if you're looking for SQ (if you're just looking for SPL, ignore everything I write...doesn't matter anyway - you'll be deaf soon enough...remember, anything over 110dB long-term can damage your hearing, anything over 120dB can damage your hearing, even short-term. These numbers do go up as the frequency goes down, because you are less sensitive to those frequencies, but I don't have the numbers.) Pioneer is also an excellent brand, but not in the same class as those three (and the price reflects it). If it fits in older models, go for the Alpine MP3 capable head; I have a slighty older version of it and it is an excellent unit. Having MP3 capability is fantanstic. This is out of your price range right now, but I would save up and do it right the first time... even if you have to run the stock speakers for awhile. Anyway, I'm not gonna ramble on and on... but that's my advice. Save up and buy a very good-quality head unit. Stick to high-quality brands (I named four, but in an effort not to offend anyone's system here I'll not name brands that are NOT high-quality, except for Sony. I apoligize to anyone that owns Sony, I hope you're happy with it. But to everyone else, avoid Sony car-audio products. I'll leave it at that.) And to answer your very first question, my system consists of:
(I don't remember any product numbers for any of this stuff and don't feel like looking it up!)
Alpine MP3 Head
Boston Acoustics 5.25" Frnt
Boston Acoustics 6.5" Rear
Audiobahn Amp connect (4 ga. PWR + GRD; shielded interconnects, etc.)
Audiobahn Class AB Mono channel amp (1801Q? somewhere around 400-500 watts at 3 ohms)
Audiobahn SQ 10" sub, .6 FT sealed box (shoulda made it just a little bigger - rolls off too quick, not as much cabin gain as I anticipated)
I haven't spent a significant amount of time working on it since I first put the system together, so it could sound better than it does. Oh well... Good luck!
Oh yeah, and concerning the subwoofer box rolling around offroad - here's what I did...
http://community.webshots.com/photo/62833728/62834558rTiesD