What's the most accurate way to time-stamp analogRead data?
There is no more accurate way of getting time on the arduino, but I would suggest you use millis() instead.

micros() returns microseconds, or millionths of a second, since the arduino was turned on. The issue is that the 32 bit unsigned integer used to store time on the arduino can only count about 70 minutes worth of micros before overflowing and resetting to 0. (see http://arduino.cc/en/reference/micros)

millis() is in thousandths of a second since the arduino turned on, and it will not reset for about 50 days. If you think one thousandths of a second is good enough resolution, it will probably be the better choice. 

If you need time to be absolute, as in the current day/hour/minute, you will need to buy a real time clock to plug into the arduino. They are about 20 bucks, and available from all the standard arduino accessory stores like sparkfun, adafruit, ect. 

On your question of the order, both commands run so quickly, I can think of no reason it would matter.