The north coast is great. It all depends on your budget and many factors and that is why people have a tough time explaining what to do. I moved to the DR and decided to stay in Cabarete as I like the beaches there. There are plenty of bars along the beaches there and its a good place to start to get used to the country. I would suggest booking a place for one month and give yourself some options in case you find a better deal or want to check out another part of the country.
If half of your ambition is also to hook up, then the beach area in Cabarete attracts lots of toursists and if you are looking for a Chica then you may find one in Cabarete or hanging out in Sosua. But, since you are new, Cabarete is the safest choice for you... When you get here and if you want to do a lot of sight seeing, there are tours and etc. you can find in downtown Cabarete an sign up to do those.... Fishing, scuba diving, caving, boat tours, zip lining...lots of stuff. A lot of people at my place like to surf in the morning and then go kiteboarding in the afternoon... Party's at night in Cabarete or Sosua occur every night...it's always saturday night!
Most people will be reluctant to advise you to rent a car because of the crazy driving done here, potential liability and more... But, after a while here you may decide to rent a car and visit some other cities on the island... Or, you can take buses to about everywhere.
Overall, you will have a very good time and it's a good place to get away from normal life for a few months and explore a new culture. Since I have moved here and despite the problems and frustrations permanent visitors encounter here, I feel free here and I'm happy. If you have some money the world is your oyster here...