1) Is Ys+ playable standalone, or does it need Ys to play as an expansion?
Ys+ only adds additional wooden pieces. It is not a game by itself.
2) I have read of people finding mold on the brokers of Ys. In fact my friend whose set I learned the game on also has mold on his, but I like the game enough to want to buy a set. Does Ys+ also have the mold problem?
My copies of both the base game and the expansion came with moldy pieces. I contacted Ystari and they promptly sent out replacements.