2002 nissan frontier overhaul

I am doing an overhaul on my Dad's truck that he has given me: 2002 Nissan Frontier. For the HU: Pioneer DEH-P5900iB Front Speakers: Alpine SPS-17C2 Rear Speakers: Alpine SPS-10C2 Now I picked the Alpines because the Infinity References I wanted wouldn't fit in the rear and I wanted a matching pair. I will be going back home on leave for a bit for Christmas and want to get this done. I am looking at an amp to power the new speakers and wanted to stick with Alpine but feel free to recommend whatever brand you happen to think would be better in this application. Now there are tweeters mounted on the plastic part above the dash right next to the windshield (sorry, don't know the name) and was wondering if I should replace them with other tweeters which would mean using crossovers? I am new to the car audio but as an electrician in the Marine Corps the wiring should not be a problems. Thanks again fellas.

Oh, by the way, this is the crew cab version.