I believe that 1 BTC-prefork = 1 BTC-core + 1 BTC-XT.
Not on a panic-driven market.
Yep. There will be chaos.
It's possible if both chains survive that it's a zero sum price game at equilibrium, but even then I wouldn't expect the panic factor to fade away too quickly and the price(s) to return to pre-fork levels in sum.