Component Setup, and Head Unit
 

Im new to the blazer seen and have a 98 blazer LT. Also new to the car audio. Im looking to upgrade speakers and head unit in my blazer to start with. Looking around I keep finding different sizes for the speakers? Am i safe with 6.5" for both front and rear doors? Can anyone recommend some nice component speakers. Im not looking for the best but dont want to buy crap either. The 2-way, 3-way speaker specs confuse me. Not sure what I would want/need. This will be my first system install so looking to do it right and have it sound good with some good equipment.
Also do I buy one set of component speakers ( for the front ), then just the 6.5" speakers for the rear doors? Will I need to buy extra wiring for the speakers?
For a HU do I go double din or single? Is this just preferrence? Searching around this forum I found this link for a HU? Is this a good HU? If I should spend a little more now for a better unit I have no problem with that. But if this will do it seems like a great price Kenwood KDC-348U (KDC348U) In-Dash CD Receiver w/ USB & AUX Input.

Any input or opinions would be much appreciated. Thanks