your system will suck if you put 6 6x9's...you won't get good midrange at all and you will get lots of distortion...6x9's only offer a little better low end but sacrifice lots of sound quality...instead, put:
2 6.5" components in front doors 2 6.5" components or coaxials in rear doors 2 6x9's below the rear window glass.
as far as the headunit...you can only support 4 channels...you could wire the speakers together but then you cut the power in half...it would be better just to run one speaker instead of 2 in that case...my suggestion would be to get a 2 or 4 channel amp to power the 6.5" components at least...
I'd go with Pioneer...I've only used them since I got into car audio and never had a single problem with their headunits and they sound great...good looking too
without a subwoofer of any sort, and using head unit power alone, stick with 4 speekers. better imaging that way, better overall quality of sound reproduction.
KISS is a better approach here, as opposed to more is better.