Definitely check the Dominican calendar (or check with a travel agent)!! Semana Santa is very much alive, and quite crazy. Many local businesses are closed, motorized water sports are outlawed, and hotels become filled with local Dominicans who party exhaustively for days and nights on end (quite similar to Mardi Gras in New Orleans)!!
As far as getting from SDQ to POP, you're definitely better off flying into POP if at all possible. If not possible, the public bus system (referred to simply as "Metro"), will cost you only 400-500 pesos/person (if I remember correctly). You're best bet for going this route is to take a taxi from SDQ airport to the Metro station, and then stand in line to purchase a ticket for the next bus to POP (there are typically 4-5 departures for POP each day - but this may be restricted due to various Semana Santa observances). Once you arrive at the Metro station in POP you can pretty easily catch a taxi to your resort (and I would highly recommend that your travel be completed during daylight hours).