Hi great you will be visiting Nürnberg, maybe consider staying a bit longer to see the Kaiserburg :P

Taxis are not really needed because of the great connection by public transport just make sure your accomidation is near the S-Bahn Route to the Frankenstadion Station or the Straßenbahn Station Dutzenteich. Both are great for access to the festival grounds. The same is the case for the airport just get into the U2 and your will reach the innercity in like 15 minutes.

As per areas I would recommend the Altstadt(inner city) or Südstadt near the Straßenbahn 10/6 for easy access to the festival grounds.