factory chrysler stereo questions

i was wondering if anyone has any experience with more modern chrysler stereos. i have a 1990 dodge pick up that has a 2000 dodge caravan am/fm/cassette stereo in it. the speakers in the truck are getting kinda worn out and i want to change them.

i bought a set of boston acoustic speakers from ebay that came out of a 2006 chrysler 300c, non infinity. there are four 6x9 speakers and two 5-1/4 round. i picked up all 6 speakers for about $50 shipped. they're all rated at 4ohms so they will play on my current stereo.
they arent here yet so i can't install them, but my question is -- can an amp be added to the stock mopar stereo that i have now, and if so, do you think i'll need it? most amps i see for sale have RCA jack input, and my stereo doesn't have the RCA output.

second question -- do you think i'll need to add a small tweeter to the trucks interior with these boston speakers? will adding a tweeter on each side of the truck improve the sound quality whether its needed or not? i could mount the tweeter right next to the sunvisor mount -- one on each side of the truck.

i plan to use one set of 6x9's in the doors (original location) and either the other set of 6x9's or the 5-1/4 round in the corner of the cab (which is also the stock location) depending on whether the 6x9's will fit back there.

i never really understood car audio all that well, and i really don't know what works with what, or what will make the truck sound better. right now it sounds pretty "flat".

is there another stock chrysler stereo that would work better than the one i have now? i cant cut any of the trucks original wires, so any unit that i install will have to be from about model year 2001 or earlier -- the "square front" unit with the 2 plugs in back.

thanks in advance for any help you can provide.

George