I second Mercy's remarks. I got married last year at Las Mercedes, I had originally requested El Convento, which I think is the prettiest church in the Colonial Zone. It was the church I most visited as a child. Anyway, it was booked for our wedding date and thus we chose Las Mercedes, which is also gorgeous and our patron saint anyway.
The church in Altos de Chavon is just lovely, but small. You can probably fit maybe 40 people. It is ideal for a SMALL wedding. E-mail me if you need more help. I can give you recommendations for vendors that I dealt with. I planned my wedding from Pittsburgh with the help of my family in Sto. Dgo. Ours was a rather small wedding, about 80 people, close friends that came from as far as Finland and, family. Good luck!!!
Natasha