yes, it is the same, because the previous sound to the "S" is a voiced sound, so the plural is voiced too ( /z/)

Yes. For the verbs that end in /p/, /t/ ,/k/,/f/,we pronounce final "s":/s/. end in /s/,/z/,/ʃ/,/tʃ/,/dʒ/,we pronounce final "s":/iz/. others,we pronounce final "s":/z/.

The (S) in question I would say is pronounced like the s in plays, yes that is correct also like the s in sound. I hope this was of help to you.