Make sure you make a reference mark on your nut (the one on the pinion ;)) and count the number of exposed threads on the pinion shaft. You want the nut put back on, as close to exactly the same position as it is before taking it off. I prefer to use a breaker bar, or ratchet to get the nut off, but whatever floats your boat. Nitrogen in the tires is supposed to be less corrosive than plain air, but you have to pay for it and you then don't want to refill with air after that or what you paid for is wasted. I still go for plain old air, it's free.