I don't know where you are located but if the tree was on asphalt in full sun, then I suspect that the roots were exposed to high temperatures that may have damaged them thus causing the leaf wilting and curling that you saw when you brought it home. I suggest that you put it in shade or partial shade for a while.

You are correct: new roots are whitish while older roots are yellowish. Dead roots may be yellowish or brown.

I would not repot now. Wait until it recovers before repotting.

I am not sure what to tell you about the kumquat. It may be dropping leaves because it is adjusting to living in semi-shade or because it is going through transplant shock. If the former, then moving to more sunlight is called for. If the latter, then more sunlight may do harm. Maybe the compromise is to move it to semi- shade.

For both trees, be very careful not to over water. Use your fingers to dig down an inch or two to see if the soil is dry before watering.

Good point about the blacktop. Sounds like a good idea to wait for repot, then.

The repotted kumquat is now starting to flower, I don't know if that is a good sign, but I think I will give it some more sun.

Is there a particular reason a move to 5-1-1 would cause shock? I.e is it fairly normal?