nice radio, it sounds like you guys have bitten by the mod bug haha. as far as running the antenna cable, you shouldnt have any issue running along side the cb cable, but a little separation will be best. your friend will be a fish tape or a straightened out coat hanger, it minimizes the number of panels that need to be removed and also helps with running cables through the firewall grommets.
as far as repeaters, i just installed pretty much all of them in Socal and check the area if im going further. its easier to scroll through and find the repeater by freq and not have to worry about inputting the squelch code.
APRS can be fun, i think only steve c, steeevo and myself run it IIRC. I have the Yaesu FTM-350AR, i have used it a few times to mark my campsite on busy weekends out at superstition and truckhaven, my radio can point me towards saved gps coordinates. Once in big bear I got a random call on the frequency i was monitoring by someone who lives in fawnskin. He was looking at
www.aprs.fi and spotted my truck driving by his house so he figured he would call me up and see how the offroading was, that was kind of fun. I dont always have APRS running, but when i do, people stalk me
oh yea, faceplate mounting. i mounted my control head above the rear view mirror using a Blendmount made for a scanguage. the main unit is mounted under the passenger seat next to the RF amplifier.