crossover use and speaker placement

1.  No.  The Extremis won't beam within that frequency range, so any aiming will more than likely be a waste of time.

2.  It will probably work.  Just keep in mind that the quality of the crossovers in those things aren't usually the best.  The potentiometers in amplifiers are usually pretty inacurate and might be difficult to dial in correctly.  And from what I understand, the crossovers in head units aren't usually very good either. 

As a suggestion though, I recommend taking the Extremis down much further; maybe to around 50 Hz and run the sub below that.  This should give you a "bass up front" sound. 

Good luck!

First, the new Alpine amp is not stable at 2-ohms bridged.  If you want to use the rear channels for mid-bass, you must use at least 2-ohms per channel.  Plus mid-bass is stereo, not mono, so if you use Extremis woofers for mid-bass (a good idea, by the way) they should be mounted in stereo such as in front kick-panels or in the doors and operated with a stereo feed, but not "aimed."  The Alpine ICE amp puts out 150 watts per channel into 4-ohms which is about perfect for the Extremis, so get the 4-ohm versions and use one on each channel 3 and 4.  Next, there is nothing wrong with trying your "bandpass" crossover idea for the mid-woofers.  It might be tricky to get set up correctly, but if the amp has a LP that will reach as high as 400Hz, go for it.

-edit- and I see Steven chimed in while I was typing.  I agree with him, 100Hz HP on an Extremis is not utilizing its full potential.  Indeed, I know at least one person who is using one AS a sub and it kicks ass ported at 28Hz.

Are you going to have any other speakers in the back?  By themselves, I don't think they would do much good except for maybe detract from your front stage, especially without any level control on it.  They will do a great job on the midbass, much better and much lower than most other midbass drivers on the market.  I say try all 3 crossover points and choose which one sounds best to you. 

The Zapco will more than likely be a MUCH better amp with much more accurate signal processing.  Especially if it is in the digital range.  The Alpine amps look nice, but I am somewhat leary of their power ratings, especially over time.  That's a lot of power to put in such a small package without having some compromise in performance.

Wow, you bought Kit LCR's to install in your car?  Well... suffice it to say I would not have recommended that.  :)  Did you actually buy the kits with the crossovers, etc. or did you simply buy the drivers?

The LCR speakers are fantastic sounding systems, but there is no way you could duplicate them in a car.  Using the same drivers is not the same thing at all, as at least 50% of the sound character comes from the crossover and the D'Appolito alignment and the way the woofers function in that particular volume ported enclosure.  You could never duplicate them in a car; well, maybe you could actually build a set and mount them in a van. 

Back to your application: mount an Extremis in each front door and basically create a 3-way set with your Focal components.  Keep the 3 speakers as close together as you can.  Set up a subwoofer with LP at about 60Hz.  Bandpass the Extremis woofers between 60Hz and about 250Hz.  HP the Focal component set at 250Hz (use the supplied passive crossover with each set.)  This should give you quite a bit of low-end punch.  I'd use one Extremis in each front door operating off channels 3 and 4 of a 4-channel amp, with the Focal comps driven by channels 1 and 2.  Don't worry about adding anything to the back doors until you get the fronts set up correctly.

Now, as to the outstanding set of mids and tweeters you have, purchase a 0.75 cuft speaker enclosure set from Parts Express or Madisound, mount your other Extremis woofer, one of the 125's and one of the Usher tweeters in each enclosure.  Port the enclosure with a 2" flared port for 30Hz.  Build a good 3-way crossover at about 400Hz/5KHz and you'll have a really killer stereo set for your home.  Just make sure your amplifier or receiver can handle a 4-ohm load since you bought the 4-ohm woofers.  Rock and roll.