The Dominican Republic is a big island. To see its different destinations at a relatively fast pace would take you at least 15 days, moreso a month. Juan Dolio is on the southeast coast, halfway between La Romana and Santo Domingo (capital city). Juan Dolio is about three hours from Punta Cana that is on the east coast. Santiago is an hour and a half from Santo Domingo (main attraction right now is the Centro Le?n). Then you have all the places of the north coast.
For what to see in each, start with
http://dr1.com/travel/index.shtml
If you will be based in Juan Dolio, you will need to have to leave very early to get in Punta Cana (which is not a place to see local culture as it is a bunch of hotel resorts and great beach extensions). But on the way, you can drive through La Romana town and also see the attractions of Chavon and Marina Casa de Campo.
Ditto for getting to Santiago, which from Juan Dolio will be at least a three hour drive.
Santo Domingo makes more sense as it is less than 40 minutes away.
If you like to get around, would recommend you be flexible in your hotel reservations, making a route and then staying two or three nights at each place as you make your way around the country.
If you don't have all that time, then my recommendation would be to stick to visiting Boca Chica, La Romana (Bayahibe, too) and Santo Domingo, using Juan Dolio as base.
Next year come back and do the north coast, including a trip to Santiago.