Infinity Crossover and sub wir. questions

Hi all, I have a couple of questions regarding the wiring of my Infinity Perfect 12.1d sub and crossovers on my Infinity Kappa 5x7's.

First, I have an Infinity  Perfect 12 dual voice coil sub. They are dual 4 ohm voice coils. What are my options as far impedance? 8 ohms, 4 ohms, and 2 ohms? I would like to get a 2 ohm impedance load to my amplifier, so I assume I would wire both coils in parallel, correct?

Second, I have two pairs of Infinity Kappa 5x7 coaxials in my doors. They came with external crossover modules on each speaker, and I am not too familiar with crossovers. I am assuming these are passive crossovers? They weren't adjustable, I think they were just crossing the incoming speaker signal into mids to the cone and the highs to the tweeters, but I don't know what frequencies they are set at. My headunit has crossover settings and my amplifier will also. That is three separate places where I can crossover the signals and I am confused at where to set it and at what settings to use for optimal sound. I don't want to get the settings competing with each other or cancelling each other out so I want to do it right. Here are a few more details about my system as it is now, if you need more information, let me know.

2003 Ford Explorer XLT, Infinity Kappa 5x7's 100w RMS in the doors, (will be amped), Pioneer deh-p7600mp headunit, Infinity Perfect 12.1d sub in a 1.0 cubic foot sealed box (will be amped).

Thanks in advance...

First: correct.

Second: Also correct.  Turn off the crossover in your head unit.  Activate the HP (high pass) crossover on your mains amp and set it to the same as the LP (low pass) crossover on your subwoofer amp.... once you get them.  Do not try to connect the sub to the HU directly.