Puerto Plata, Playa Dorada and Sosua are all located on the Northcoast. The main highway runs along the coast which means generally in an east/west direction. The airport, although called POP is just west of and is extremely close to Sosua. When you leave the airport to go to Playa Dorada you are travelling west. If you continue west past Playa Dorada you will come to Puerto Plata. It may help to look at a map online to orient yourself.
To answer your questions, Sosua is east of Playa Dorada. If you are going to try to take a guagua or publico you walk out of the main gate and cross the road to get the easterly traffic.
As I have stated in another post on this board, you can take a guagua or publico, but this assumes you know where you are going. For a first time traveller I would recommend you hire a cab. For RD$350-400 they will drop you off at the beach entrance and pick you up at an appointed hour. DO NOT PAY UNTIL THE RETURN TRIP!! Many posts on this board have warned about the hazards of renting and driving in the DR. You are much better hiring a cab or taking local transportation. It is safe.
Once you get to the beach you rent chairs from the guys on the beach (RD$20-35 depending on your bargaining skills). They will also bring you drinks, food and any other necessaries.
As far as the PD beach - I don't care for it personally. The beach is more exposed to waves and there are rocks but no reef to speak of. The beach is narrower and not orientated for maximum sun if you are serious about tanning. There is no scuba or snorkelling to speak of.
The beaches about 11 kms. further east of Sosua around Cabarete are excellant for windsurfing, surfing and similar activities, some of which are attempted at PD but without much apparent success.
If you have more questions feel free to email me. Also, see my recent post on this board about local transportation. It's cheap, fun, safe and gives you an inside view of the people.
