For the alternative beaches, they are not far away, If you like walking it can be done by foot, or rent a car for a few days, make a daytrip to Agia Galini or to Rethymnon if You like some more shopping. Anso travel in Plakias rents bike if You like that more thans a car.
Have fun there and enjoy your 18 days. We were in Plakias in april With Easter and had almost no wind on the beach.