a great link that can answer a lot of questions you might have: http://www.mp3car.com/vbulletin/advfaq.php
for your car, you are going to need a different amp-- that particular deck you have powers the speakers, so removing the deck will remove the factory 'amp'. the amp that you get could be anything from a Focal or alpine model, or a motorcycle amp off ebay(usually about $30-50). the motorcycle amps are reported to be at least as good as the factory decks(though i don't have one, so i can't confirm this...)
the link doesn't work for the harness your talking about, but i believe that it is a harness that would be use to attach a aftermarket stereo-- you could connect that harness to the motorcycle amp to power the speakers.
for power, the absolute best way is a fused line off the battery, and i would never recommend connecting to the factory wiring for power(for kicks once, i tried it with a m4 and blew 4 fuses...)
the factory stuff was never designed to operate anything other than the factory stuff.
also, i have seen it more than once where a single 10 amp fuse labeled for the radio powers more than just the radio(in my car--mitsu eclipse, it powers the dome light, radio, and time display), so you would also need to take these other devices into account also.
so if the power supply draws slightly more, you will either be blowing fuses, or melting wires. when you pull your own line from the battery, you know exactly what size wire it is, the fuse size, and the max draw of the line(or can at least determine the max draw).
time for 2k1toasters artwork
also, the chimes are part of the radio--so you remove the radio, and the chimes go away for all functions(seatbelt, door etc...). there are modules to get them back, but they ain't cheap...