how much do you think it would cost for one person to spend a month in Warsaw?
Have you ever been as a tourist to another big town, foreign country? I guess the costs are similar, Poland is cheaper than most of European Union, but not that cheap as one could immagine. It really depends on what you're going to do here :)
And I'm sure there were some threads here on these forums where people were saying how much they had spent travelling to Poland, so browse through this section (Poland Vacations & Travel
) or use the Search function.
Would you suggest to bring mostly cash? Or will most restaurants, shops ect. accept credit cards?
CC are OK, but I have no idea how much your bank charges for conversion to another currency of payments made with a CC. I'm no expert on those hidden extra fees, because I've only used my CC in Poland so far (but when I was buying from abroad and the payment was made in Euro, my bank charged the exact amount of Polish currency I was expecting, so I hope you'd be fine).
Of course you can bring some cash too (dollars, euro) and convert them to Polish złoty in a kantor
(full name kantor wymiany walut
) to use this cash in places where you can't pay with CC (small shops, popular in Poland, kiosks with bus/tram tickets, railway stations except those big ones in main cities. Generally smaller cities and most villages don't have many facilities where you can pay with CC, except maybe tourist places, so it really depends on where you're planning to go, if you're staying the whole month in Warsaw, you'll get by without much cash, because you'll always have a choice between places that accept CC and those that accept only cash).