Laneej,
I have used many times Guido Perdomo in Sosua but I also know Guzman is good. You can trust both attorneys. Make sure you use a reputable attorney.
As for researching, most people (including myself) would suggest realtors such as Century 21 Dean or Anabela, Hispaniola Real Estate (Werner), Property Centre (Ty) and some others. Posters, can you share good experience?
As for buying a finished home vs contruction, this is a personnal choice. I have done both. Construction can certainly give you more headaches than buying a finished home. Sure, if you build you can expect greater appreciation of your investment and save some money, just like everywhere else. This is a personnal choice.
Good luck in your project and feel free to use the people of this board. email me if you have more questions.
Eric Carignan