I am pretty sure you can't cash profits out into your currency account without closing your whole position, unfortunately. (This means selling to zero, overshooting can keep the position open).
You should be able to pull out approx currency account balance - position size/leverage (though I recommend keeping a bit more than necessary so you don't immediately get liquidated if the market moves against you).
Withdrawal limits are a big problem. They have always gone through in less than 3 days for me, usually around 24 hours. Technically, it is Gox's "fault" but zhou should really implement a separate withdrawal wallet for this situation.