I have a 24" monitor and use it for both working and gaming. My only concerns with getting a 27" monitor would be that I would want to sit further back from the screen to avoid noticing the lack of quality on such a large screen. If you want a 27" I would get a 2560x1440 monitor.
With a 120hz monitor, every thing is a lot smoother, more fluid, less input lag, virtually no screen tearing and with work or just on desktop you can notice the difference with a 120hz monitor. Watch this video I know he blabs on about all the features but he does tell you the benefits of 120hz.