There are several options to get from the airport, including public transport (each international airport webpage of any airport will lay out all the options)
Look into the Krakow Card and see if it's a good value for you based on the price. The 3-day version of the card says that all public transport is covered, including from the airport. The public transport in Poland is very inexpensive in general. The museums, with some exceptions, are unusually inexpensive. I'd caution getting this type of tourist card for the city (it's pricy for such an inexpensive country) unless the math makes sense and the value is greater to you than the cost (since it may be much cheaper if you price everything out separately). I wouldn't worry too much about making change, it's not that difficult. Also, most of the town can be seen on foot.
You're staying in Krakow a really long time (it's very compact), so consider some side trips (aside from the obvious). Maybe even Zakopane or Częstochowa (if you're interested in seeing the Black Madonna or have interest in Catholicism)?
Hopefully you'll come back here and post on your trip once you're done. I'd love to hear a 6-7 day itinerary of Krakow because it's a bit unusual.