As far as I know you won't have any problems. This is not from my experience but I think it's pretty much the same as flying here in the Slovak Republic. Here there is no problems with ATC and all heights are in feet. I was looking in the Bottlang for Poland and it seems fairly straight forward, it states "Non commercial non scheduled flights of foreign aircraft do not require permission for entry and operation, assuming that the aircraft is registered in an ICAO member state". While you are in Poland why not visit us in Slovakia for a bit more of a eastern european experience. Have a good trip.