Question 1.
Are your Bostons 2 way (mid and tweeter)?
If so, you dont need the Kappas up front. In fact it might sound a little weird, since you will have the same sound coming from 2 different places. In other words, the mids and highs coming from the 2 speakers will be out of phase.
IMO, if you have good door speaker, dash speakers aren't needed. unless its a center channel only.
Question 2.
What are the ohm ratings on your speakers? The head will not like anything much less than a nominal 4 ohms at each channel. Where some amps are rated to handle less load, head units typically do not fair too well when set up like that.
I have no clue how the concert sound is wired from the factory, but I assume they use 8 ohm speakers and wire them in parallel to get a 4 ohm load. If you use the factory wiring, using new speakers (which are typically 4 ohms) then the head will see 2 ohms. You dont want that to happen. The internal amp will not last long at 2 ohm loads.
The stock deck power will be enough to power the speakers without an external amp. However, you might want a set of bass blockers (or similar capacitors) to roll off low frequencies to the front speakers.