I've flown through Poland VFR many times over the last 10 years or so, on delivery flights from Lithunia to UK (no points for guessing what type). Most visits were to Gdansk, Posnan and Szceczin (I know the spelling is probably wrong).
A few tips you might find useful:
1. If you are flying VFR you should follow the airways routes (VFR route maps are available at most places) as long as you don't accidentally fly through "sensitive" areas you can deviate.
2. Heights are in metres and should be annotated as such on flight plans. Most of my flights were filed for 600 metres.
3. If you are stopping somewhere just for fuel, go and file the flight plan first, then refuel the aircraft (there is no Polish word for quickly) as it will take a little time.
4. There is no real radar cover, except in the vicinity of major airfields. You can fly for hours without talking to anyone. I used to fly with 121.5 dialled up just in case.
5. Hotels a very cheap and the people a very friendly and helpful.
6. US Dollars are accepted everywhere.
It's about a year since I last went through there but i hope this helps.
Have fun.