Is there any way to approximate how many shadow bids/asks are hiding in the orderbooks? Or at least find out after the fact? Just watching what effects the bitfinex price makes me skeptical that the visible walls are at all representative.
I don't think there is any way to find out anything about the stop buy and sell orders on Bitfinex. However, there is information about how many Bitcoins have been lent out for leveraged trading.
https://www.bfxdata.com/