1) Where does this blight come from, the box or the 5 per player placed on the flipped card?
The 5 per player on the flipped card. (Unless it's during setup or explicitly stated, Blight always comes from the Blight card and returns there when healed.)
2) Are the beasts destroyed from any land or only if they coexist with buildings? The syntax on the card is unclear.From any land.
The second one was already a FAQ. I'll make a FAQ for the first question. EDIT: Here is the new FAQ.