That Kappa Five amp looks like its going to eat up a a lot of your budget, looks like a nice amp though, some guys are talking about it here. You can find some great deals in the classified section for some amps. Subs look good, just be sure you have a proper enclosure. Can's say anything about the headunit becuase I dont run one 
Most people around here don't run rear speakers, there is a bunch of info on this forum all about this i.e.: http://www.diymobileaudio.com/forum/product-selection-comparisons/9806-rear-fill-do-you-use.html. You have a Trailblazer so you may want some for your rear passengers, but the option is there to just run front speakers.
If you do decide to run just front speakers your amp options get a little easier especially if you want to keep it simple and run just one amp. Omitting the rear speakers will also free up some budget.
If you decide to run rear speakers.... please please please put most of your speaker budget into the front ones, those are the ones that count. You will want to run the rear speakers attenuated anyways.
Most people around here don't run rear speakers, there is a bunch of info on this forum all about this i.e.: http://www.diymobileaudio.com/forum/product-selection-comparisons/9806-rear-fill-do-you-use.html. You have a Trailblazer so you may want some for your rear passengers, but the option is there to just run front speakers.
If you do decide to run just front speakers your amp options get a little easier especially if you want to keep it simple and run just one amp. Omitting the rear speakers will also free up some budget.
If you decide to run rear speakers.... please please please put most of your speaker budget into the front ones, those are the ones that count. You will want to run the rear speakers attenuated anyways.
