Re: turning to stone: wouldn’t it be cool if Medusas (or spellcasters) could choose what kind of rock to transform their victims into? That would be a plot driver, especially for the snakeheads.
Via intermediaries, victims turned into precious metal ores or gemstone then broken up could be sold to finance a variety of things. Deep dwarves or Derro allied with a Medusa could fund all kinds of stuff.
Good way to set up a salt merchant, too...