I just don't trust myself to not scratch something or breaking a clip on the door inner panel on a brand new car. I am plenty handy and capable, just don't feel like the risks.
I've heard not to bother with the tweeters for reasons ranging from the midranges in a decent set of door speakers will be fine, to the difficulty of accessing them and the short wires with no slack.
I have a highly rated set (at Best Buy and Crutchfield) of 6x9 kickers for the doors and 6.5" kickers for the back. I have an existing Alpine Amp for the main speakers and a sub box w/ 2 10" woofers in the very back with it's own small amp.
If I join Best Buy's Total Tech ($200/year) they wave all their usual amp/speaker installation fees, save for wire and possible brackets (around $80 they say) which would bring the installation cost in at around $300. I paid $100 for the speakers, so the grand total would be around $400.
I've heard many people say that while the built in upgraded/package Harmon Kardon and the add-on Rockford Fosgate upgrade package are both better than stock, neither are all that great. My amps definitely are capable of loud crisp sound, so if these Kicker speakers are decent, than I think I'll be in good shape.