Planning on putting a good system into a old truck and could use some simple advice!

Alright, so I consider myself somewhat of a music connoisseur and that has led to me being audiophile, but I don't know what "specs" to look for besides reading reviews on products. I am a quick learner (EE student as well,) but I know jack about car stereo systems and what the terminology implies (watts, channel, amps, component/coaxial speakers, ect) in sound quality sense.

So, I would appreciate some advice on the basics of having a full audio experience in an old truck. My truck is a 1997 Dodge Ram, and from what I can tell it has stock speakers. I put a Sony stereo in the truck about two years ago. I am guessing its the basic 52W x 4.

Before I begin, being a student, I live on a tight budget budget. This affects many of my decisions.

In my quest for a good sound system, I thought, replace the speakers next. I saw these Sony XS-GTX6931 speakers got good reviews and were cheap. I got confused with the names of speakers and their importance (component, coaxiae, ect.) What would the four speakers in my truck be called? I also found an old amp in my brothers truck (Rockford Fosgate 250 aII) that I could use (does this improve the sound quality?) It is two channel, what does that mean in regards to the number of speakers in my truck? I listen to mostly country and music lighter on the bass so I wasn't planning on a sub unless it would really help.

So, if you audiophiles could give me some sort of direction to a decent sounding system with the supplies I have, I would greatly appreciate it!

P.S. Would having a "tweeter" speaker help, and could it be added to the other four if the radio is only 52W x 4?