I also am going figure out how to keep so much change on me to use..
If you're in a city/town and you see a shopping centre (mall) (in Polish it's Centrum Handlowe) they will have toilets and they are free of charge. So that's a good thing to remember. If you need the loo very often you should be ok as long as you plan your itinerary very carefully and identify all the possible toilets in the vicinity before you go somewhere.
Will credit cards be accepted or debit cards in Poland?
Yes, almost everywhere but it's good to have a bit of cash if you want to buy from a street vendor for example. Be careful about additional bank charges when using your card abroad, especially commission when drawing money from ATMs. Check out the terms and conditions of your card provider before you travel. You can change cash in Poland at a 'Kantor'.
I'd invest in a pocket sized phrase book if I were you. It can come in handy. If you have to talk in English, keep it very short and simple. Don't worry about sounding polite. Polish culture is very direct and Poles have very little patience. They don't want to hear a long rigmarole. They just want you to get on with it. Just stick please on the end if it's a question and that will do :)