Interesting.
The Kappa series is a pretty good series. I think theres better for the money, but thats a new thread
If I were you, I'd dump any thought of rear fill. Run eithr the 2 way's or 3 ways, it shouldnt matter. The 3 ways could probably handle a bit more power. Also, PPI is a strong amp name, but not as strong as they were in the early 90's. Still good though. You want 1 channel on the amp per side of components.
Thus, 1 component set (Left & Right) you want a 2 channel amp. Most aftermarket amps wont have a problem running the resistance the speakers provide, so dont worry too much about speaker resistance until you do a sub.
SO, it sounds like you just want some better sound, not to actually compete. Thus, IN YOUR CASE, rear fill is up to you. Generally, competition systems want zero rear fill as the point is to mimic being at the live performance, where everything would come from in front of you.
As for tweeters, I would DEFINATELY change out the stock tweets. Heres the deal that everyone overlooks. Everybody spends countless hours deciding on a sub, then runs out to the buy the first component set they can find. Heres food for thought. Its much MUCH easier to hear distortion and other artifacts in music in the middle to high frequency range then it is in the low range. So, shouldnt you spend more time on selecting mids and highs? Yep
Swap the stock tweet, if its high on the dash give it a 10k hi pass, run the comps in either factory or preferably kickpanel mounts. You could keep the factory tweets up high, then run the comp set together (The ideal scenario, as it blends better) But still, any tweet mounted up high, if it was me, would have a high pass X-O set very high (10 or 12K) or very little power.
SO! To cut to the chase...
I'd buy 1 set of components, and a 4 channel amp if the price was right. From there, you can throw some midbass in the back later if you'd like. The 4 channel amp gives you flexibility. Personally, I'd find the cheapest amp that gives you the power you need. Essentially, amps are pretty much the same. Watts are watts. Anything other then the flea market crap (Pyramid etc). JBL comes to mind for a good budget amp. Run 1 4 channel amp, 1 set of components and the optional tweet is up to you (As far as up high)
My 2 cents.
^^Why the hell was I thinking components? *L* Either way, I'd do the 3 way if I were you. If you can, go audition them somewhere. Speakers sound very different, and you have to find one that sounds good to you. Anyways, 3 way.
Components...Jeez....Off to find coffee......