2. You should be able to, but : -
In a dry or semi-dry dish threads need to be soaked in a little warm milk before use. (Add the milk too.) No need with powder.
Saffron is the world's most costly spice. Is is much more difficult to counterfeit threads than powder. Only buy powder from a reputable supplier. Buy threads from an Indian grocer if you can - saffron is used in India more than elsewhere.