How do I decide if 14ms response time in IPS LCD monitor enough?
At 14ms, you can still get an effective 71 frames per second.  It should be fine for working with video.  The frames might not show up exactly at the start of their time interval, but it still should be ok.  

Faster response is still better, but it isn't going to be critical for anything other than really high frame rate gaming.  5ms is very VERY fast for a high end screen.  Cheap screens go faster because they use simple techniques that are fast and cheap but produce (greatly) inferior image quality.  Better screens like IPS and PVA are by nature slower and the last time I was seriously in the market (which was a couple years ago), 6 to 8ms was considered fast for an IPS or PVA.  sub-5 is completely unnecessary.  14ms is probably on the slower end, but should still be fine.  Even 20ms would likely be ok, though it might start getting more noticeable.

As far as if ghosting would be an issue, at 71 refreshes per second, a frame won't be able to off by more than 1/3 or so of a frame.  That's 1/90th or so of a second, so would be pretty minor.  It might make for a slight stutter, but isn't that likely to be noticeable.  I think most of the arguments against it come from the faster is better mantra and the twitch reflex crowd.  You might or might not be able to notice the difference, but it shouldn't be a significant problem and I'd personally much rather have a good quality display with a slower refresh than a display I can only view from one exact angle and even then have color differences from the angle of one eye to the other, but have "crisp" frame rendering.