Silence- and silence+ count as silence for goals. Same with block, silence, and all other things that have a + and - version.
You can't die the first time you reach 0 HP, only any subsequent hit can kill you, so just play it unsafe and you should be fine :)
Yes, but then you "lose" the character when they get kidnapped, and since the cursed knife is 100% kidnap chance, I don't want to risk it. By the time you can rescue the character and uncurse all their gear, and uncurse their class to change back to anything else - you've basically "lost" the character for ~10-20 runs of carrying a dead weight. (Cow and Prisoner are useful at tier 3, but fairly dead weight in a party until then.)
That's why I'm so afraid of "losing" my Rogue, just barely managed to get her to Tier 4. (and now have a whole new curse to remove....)