Duuble din head units are nice but in my opinion they arent really worth the money (to me they are more for show) anywho...fosgate speakers are a quality speaker. The best way to buy speakers though is to go down to a local electronics store (best buy or similar) and listen to a bunch of differnt brands/models of speakers (definitly look at the Polk Audio MM series). Everyones ear is different, so what sounds good to others may not sound the best to you. For your amplifier try to stick with Class D amps, they will run more efficient and cooler (Alpine is a very good brand). If you want tweeters then buy a component set (these will come with tweeters, door speakers, and crossovers).
My set up includes, pioneer head unit, Focal components w/1" tweeters and 6.5" door speakers (had to modify the door to fit) up front, 6x9 Polk Audio MM691 in the rear (again had to modify the door). These are powered by a Polk Audio PA660.4 amplifier. Also have a 12" Rockford Fosgate Punch HX2 subwoofer powered by an Xtant 121M amplifier. To me this sounds great.