Do you normally trade stocks with news? Personally, I pull stocks with news, so I can't comment on how you would decide what is a gap that is 'too big'. That implies that news interpretation is part of your strategy. Is it?
I never adjust my prices or skew my envelopes.
As to systems going down, yes it will happen to everyone eventually. Make sure you have the phone # of your trade desk handy or on speed dial so you can at least place some stops. My spreadsheet keeps running after the opening bell and tells me the fills that I should have gotten and what the p/l of each position is. It's handy to see if you missed a fill you are entitled to, but also if you do go down, you can call and tell the trade desk what orders to place right away and not have to wait for them to tell you all your positions.
I never adjust my prices or skew my envelopes.
As to systems going down, yes it will happen to everyone eventually. Make sure you have the phone # of your trade desk handy or on speed dial so you can at least place some stops. My spreadsheet keeps running after the opening bell and tells me the fills that I should have gotten and what the p/l of each position is. It's handy to see if you missed a fill you are entitled to, but also if you do go down, you can call and tell the trade desk what orders to place right away and not have to wait for them to tell you all your positions.