The signal assembly is a dealer part. Not cheap. I would definitely do an electrical troubleshoot to make sure the LED assembly is bad before replacing. If replacement is necessary, side mirrors are not expensive. It would be more economical to find a complete side mirror and replace the whole thing. It just depends on what your time is worth.
The mirror is attached to the door with 3 nuts. Pop off the plastic cover in front of the window to expose the nuts, take an electrical connector loose, and remove the nuts. Swap mirrors, attach the nuts, plug it in, snap on cover. Voila, new mirror.
That really depends on whether it is the "Change oil reminder" indicator or the "Low oil pressure" indicator. If you drive the car without oil pressure, it won't live long. As new as this vehicle is, it is probably low on oil. I check mine once a week when I get gas.The oil should be changed at least every 5000 miles; if yours is low it would be a great time to change it. Less used oil to catch and dispose of.
You can Disable that warning. The body shop probably unhooked the battery and this reset the warning. In any collision, the body shop is supposed to have a mechanic check the rest of the vehicle. Take it back to the shop. The temp sensor could be having issues on the air flow sensors.