Good info.
But I would prefer to take a publico to the Sosua terminus then catch a publico to Gaspar Hernandez from the immediately adjacent parada. Likely to be quicker overall despite the change of vehicle. The Rio San Juan guaguas make many more stops.
I would do so because, boarding the publicos at the start of their routes in to Pto Pta and Sosua, I can buy both places in the front seats for more comfort.
If you are on such a tight budget that 100 pesos is important to you, then the guagua is the answer, but allow plenty of time.
Incidentally, I have never tried to buy two seats on the guagua for comfort. I have a feeling it would not work out too well.