You can get cash from ATMs around the city using VISA or MasterCard. The ATM fees and exchange rates are good. You can exchange cash in dollars or other foreign currency at Kantors located almost everywhere in the city. Their exchange rate is also good. Travelers checks receive lower exchange rates.
Hotels provide terrible exchange rates.
It is safe to walk around, day or night. But every city in the world has pickpockets, Krakow included. When in doubt, walk with others. We will have Internet access at the conference site. Don t expect your hotel room to have a modem port.