Welcome to genvibe.
There is a bulb in the shifter. There are two approaches to replacing it. One is shown in the video that theamdman linked at the end of
viewtopic.php?f=20&t=33701 The other is pushing on and fidgeting around with the PRNDL plastic strip and get it to move out of the way to gain access to the bulb. The first way is a lot more involved, but the move the strip method can really be frustrating trying to get that plastic strip locked back into position.
Not shifting normally at cold start might be normal, the electronically controlled tranny tends to shift at higher RPMs when cold, probably to help the engine get to normal operating temp sooner. I don't remember worrying about keeping it under 3K when cold, partly because a tenth of a mile from when I leave my house, I have to turn onto a 50 mph road and go up a hill, so I usually have to punch it pretty soon after start.
fueleconomy.gov says the highway mileage estimate for an 04 AWD vibe is 29 mpg, and I'm fairly confident there's not much you can do to get anywhere near the 40 you got with the civic. My first was a manual tranny, and over 288K miles, I had one tank where I hit 40 mpg, that was coming back to sea level from the mountains. To be honest, I think the time and effort required to somehow get 40 mpg out an AWD vibe would be better spent on a different car. Somethings might help, such as a more efficient exhaust might help, not sure the money spent would ever equal the cost of gas saved.
I don't remember anyone installing bigger side mirrors. Maybe some trailer towing vibers have, but I don't remember. I also have an 03 Tacoma, and it sure looks like its bigger mirrors would fit a Vibe, but I've never taken the truck mirrors off to see. If I get rid of the truck before the Vibe, I might try it, because the truck mirrors are bigger and are also the swing away type, looks like the same mirror control in both. Don't buy some based on that, and I'm not likely to test it myself anytime soon.
I don't know why madstyle didn't host the wiring manual, probably just lucky he still has the repair info out there. I don't know what the copyright issues are on that stuff. There used to be various sites that hosted the zip file of the full matrix manual, repair, wiring, and new features, but I can't find any online anymore. I haven't seen a Vibe parts list on line.
There is a pdf of 03 matrix parts at
http://www.genvibe.com/images/misc/manu ... atalog.pdf You'll probably have more luck finding Matrix parts these days, Toyota is supporting their version better than GM. A/C parts are different though, and obviously exterior body panels, probably a few others