Questions for Cocodrilito
These factors will affect your trip:
For how long are you coming?
Is mainly a sex trip or a tourist holiday with a bit of sex as a side dish?
Do you speak Spanish?
If you do not speak Spanish and are coming for less than two weeks for a sex trip, I would forget visiting Samana and other places. There is plenty to keep you occupied in Sosua and nearby places like Puerto Plata and Cabarete for up to two weeks on a first trip.
Learn to handle yourself in the DR without getting ripped off or endangered this trip and do the tourist stuff another trip.
If you already hold sufficient euros, then fine. But if you have to change from zlotys then I would change into dollars. You may want to bring a bank card as emergency back-up.