I'm a bit of a coffee 'purist' and I like to grind my coffee before brewing it to preserve taste, texture, etc. (I also only drink it black, but that's beside the point).
Also, should I bring my grinder or is such a device readily available in Poland?
Hmm, I only know of at least seven places where such a device is available in Warsaw. Perhaps you should bring your own.
As for beans, they are so common that the nearest place which sells beans is no more than 100 metres from my apartment. They do sell Hawaiian Kona and have three different roasts of Ethiopian Harrar but they kicked me out of their shop when I asked them for Blue Mountain (asking for it was a joke but the owner didn't think it was at all funny).