how much 'play' you leave depends on the margin computation of your broker and your positions. for something very volatile like occ-tims or span, i only use about 5-7% of available margin. for ib's pm, i would use about 15%. for reg-t, i'd use more because it's fairly stable. the other thing is, i trade index options so i don't worry about assignment.
I know your situation is slightly different, but just in general: 1) It's a very difficult to trade options as a retail when market makes large moves. For example the es option market is pretty much nonexist when the sp500 was gapping down 50+ pts, the bid/ask spread was all in the 10-40pt range. Only the front month atm strikes has some acceptable spread. 2) It's the worst and most likely time you will get liquidated from IB. Really is a nightmare because there is no market and IB wont let you do anything to adjust. So all you can do is watch as it close your position at MARKET when the bid/ask is 40pt wide. 3) This is a hard lesson, always make sure you have plenty of excess liquidity relative to the positions you held. Especially when the market is violatile. 4) The only emergency recovery i can think of is a direct wire transfer from your bank to IB, to bring excess liquidity back up so you can close out the position YOURSELF by doing limit orders instead of the IB engine at firesale.