Yes, you must pronounce the "Z" & "S" sounds exactly as written (e.g, as in "zoo" or "silly"). The first letters—"S" & "C"—are both pronounced like "S."

yes , there is a difference.

Yes, the S hisses--there is no voice, just a hiss. The Z hums and hisses at the same time. The "z" is "seize" is just as loud and evident as it is anywhere else.

Yes - as Brad has pointed out, the Z in seize and the S in cease are pronounced as written. http://howjsay.com/index.php?word=seize http://howjsay.com/index.php?word=cease