When using the tram you can buy ticket before you get on or on the tram but always remember to verify it in stamper on board.
Tours to Auschwitz are available when you arrive with collection from your hotel. I would advise to book with a guide.
DO NOT use the taxis outside the airport as they are extortionate! Download Uber on your phone, they cost a fraction of the price.
Food and drink in Poland is cheap so you wont need to change up much money.
Visit the Jewish Quarter. It is an area that is magnificent in sights, the huge church is a must! Local eat at the market center.
I loved Poland and would recommend it to anyone. You feel very safe there too.