Mid May, use to be reasonably warm (between 15 ^oC and 20 ^oC) and sunny, but watch the weather forecast before arrival. Due to weather change it is impossible to say anything for sure. Weather is very impredictable, You can expect both tropical warm, and arctic cold with snow falling.
Raincoat may be useful, especially for the field trip.

Currency are Polish Zloty's - exchange rate is about 4 PLN to 1 euro.
It can be exchange in hotels and number of cambio - offices in the downtown.

Lunches and dinners can be found in the variety of restaurants in the vicinity of IOPAS and Sopot downtown (download map).
Lunch may cost anything between 10 and 50 PLN, dinner 50 to 150 PLN.