I'm sorry about Eva from Florida.
Plock is about 100 kilometers (yes, we use metric system :) ) from Warsaw so it would take about 1,5 or 2 hours to get there by car or train. But travel is not a problem. You should think abuot find some people who could help you there. Poland is a little bit diffrent than USA :). It's hard to rent a car here, so I suggest train or bus. Then you should have room in hotel reserved and it may be problem in small towns - accually Plock is quite big city so there should be some hotels. As you said - the biggest problem is language. Old people don't know english at all. Young generation is a little bit more educated but you should have a translator with you anyway.
But this is only my opinion and you may find very kind people in Plock and Brzezno and find your roots. And it would be great adventure :).
Why don't you try to send an email to any Plock or Brzezno department of administration? They should know english and send you some information. It's good to know who and where you want to find.