So the first problem is solved: I was trying to pass the private key in as a string, not a PrivateKey object. (Would probably be nice to have a graceful error message for that). I think dsteem isn't encrypting memos that start with #, although it's a little bit hard to tell because the steemitwallet website isn't displaying anything and I can't tell if that's a problem there or if it just doesn't like to stay logged in.