Back in the dial-up days, when it came to taking out Ts and CTs, you made do with an IBM Model M keyboard and Honeywell disc mouse. Over the last decade or so, peripherals that glow like psychedelic double-rainbows and sound like 50-cal. machine guns are all the rage. And the settings you can tweak — DPI, mouse sensitivity, USB rate... being a pro Counter-Strike player requires tuning your gadgets and now you can benefit from their knowledge.
While everyone has their own preferences when it comes to mouse settings, CS:GOpedia is an excellent resource if you don't know where to start, or just want to compare peripheral sensitives.
The site currently has a database of 225 professional players that not only catalogues the settings they use, but hardware too.
In terms of mouse/keyboard/headphone/monitor recommendations, sponsorship deals muddy the waters a bit, but when it comes to preferred DPI and mouse sensitivity, you're unlikely to see compromises.
Of course, I wouldn't go changing your DPI from 400 to 1600 and expect to get headshots from the hip using a Scout (RSI is a thing, too), but if you're looking for an edge to improve your game, this is as good a place to look as any.