Actually components are techinically a 2 way. There are also three way components. All that means is in a 2 way you will have a tweeter and a woofer. Each will play its own freq. I think what you mean is coaxial. That is then the tweeter is mounted right on top of the mid. Typically these are cheaper because the materials and crossovers are not built as well. I think its a good idea to go to as many shops as you can and jsut listen to all the different speakers. It ill give you an idea of what you like and what you dont like. It will sound different in the car but atleast youll have an idea.

Also the more "ways" a speaker has does not nessessarly make it sound better. Just because a speakers is a 4 way doesnt mean it will actually sound better then a 3 or even 2 way.

The last thing is I would really reccomend a amp on the interor speakers. Headunit power is way over rated. Most of the time those 50x4 head units will put out maybe 22 or so. What price range are you looking at for amps? I dont like rears but if you really have to i would just go with a set of coaxils and be done with it.