[1986nate]

The mileage won't matter for what spark plugs you choose (at least it honestly shouldn't). I would advise against the K&N if it is one that is reusable and has oil in the filter as the oil is "sucked" into the intake and coats the MAF causing the ECU to get incorrect airflow readings.

The low gas light does not operate in the same fashion as the guage and so the light should come on as normal. If you are too concerned, in the next couple weeks see if you can fill up your tank, drive as much freeway driving as possible. Drive for about 100-150 miles on that tank and then refil it. Make sure you use the trip and when you refil it, check your gas mileage (miles divided by gallons) and this will tell you what your mileage is. This in turn you can use to figure out about how many miles you can go before your gas tank would be low. (about 18 gallon tank)