You may need to fly to Warsaw and then take a domestic flight to Cracow or switch to train. The InterCity train takes 2h40m. Advise the organisers on your arrival time so the bus can be scheduled accordingly. The participants will be accommodated directly at the conference center. There are only double rooms.
All rooms have private bathrooms.
Unfortunatelly, there are old and new 100 zloty notes. As most payments are made in cash in Poland, you are advised to exchange some money. Check with your local Polish consulate if you need one. It might rain, but the weather is usually nice. If you need hotel reservation in Warsaw contact the organisers directly.