We were in Poland last month and had a wonderfull time with my relatives. You can spend a few days in Krakow visiting the Old Town. There are many places to stay there and we found a nice apt which held 8 of us for a relatively sheap price. Everything you want to see is witin walking distance or a golf cart ride.
Auschwitz will be a full day affair and it may be easier to go with a tour from Krakow to be part of a group since they require guides to keep the crowds moving smoothly.
I would heartily suggest that you spend some time in the Zakopane mountains. The village is a great place to visit, the peaks are on the border with Slovakia, hotels are fairly new and cheap. The cable car ride to the summit is great and you can eat at the peak. Once at the top you can hike for an hiour along the ridge. Many people ride one way up the cable car and hike down the trails back to the base of the cable car.
I do not know if you are going by car or train. Poland is in the middle of building and modernizing their highways. Krakow is very congested because of the construction. The drive from Krakow to Zakopane once you leave the city is pastoral and part of the beauty of Poland. Driving from Zakopane to Auschwitz will take a few hours since it is via local roads.
The Krakow train station is near the old town and I did see rail lines to Zakopane. Polish rail service is being upgraded, but is not yet at the level of what you will find in Western Europe.
Travel very light if you take transit and enjoy Poland. It is a very optimistic place now and full of color instead of being black and white under Communism's boot.
Make sure that you have a GPS . Most young people know English. However, like any other country, talking in the native language in greeting someone will open people up. Watch out for Gypsy scams.