Wow I just got a headache from reading this novel.
Anyways, congrats on your new Maxima.
First off I have a DEI remote start and am very happy with it. As for your factory alarm remote have you tried changing the battery. Since it's working close range and not far away sounds like a weak signal. As for the system you may seek more info from the following sites:
www.maximadriver.com
www.maxima.org
http://forums.maxima.org
They are great sites to start at and also have many links.
You might try posting on the forums at the Maxima.org you may get more responses/opinions about all of your questions. There is an audio/eletronics page where you might get info on stereo system.
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Stillen kit & grill, Stillen Type II spoiler, KYB AGX/Progress, 19x8.5 ADRs w/Toyo Proxes FZ4s, ...........