For gaming, the tool of choice is the mouse. A mouse can make the difference between sucking, simply doing good, or actually being able to progress in ability IMO. A keyboard can be as fancy as you want but really there is nothing to it unless you play MMO. That is when macro keys can come in handy. I have gamed on both a mechanical a regular "gaming" keyboard (my Lycosa, Saitek, Fatal1ty, ect), and 2 dollar garage sale specials. None of them made a difference in my gaming ability. Expensive keyboards IMO are more geared toward typing ability. If you wish to get a "gaming" keyboard that is up to you.
I have used a Razer Mamba, Lachesis, Deathadder, and Naga. I did not like any of them. Not because I thought they were crap, but because my style is palm grip and Razer mice are more geared toward claw grip. I also like meaty mice with weight. Most all Razer mice are exceptionally light.
I have used the G700 (current), G9x, G500, G5 Rev 2 (basically same mouse), G5 rev 1, MX518, MX510, and some cheapo. The G5 was my tool of choice for the longest time until I got my G9x. It was "too small" for me as the style of grip is much different than traditional Logitech mice. I finally got the G700 and I love it.
I say go to Best Buy or any electronics store with keyboards and mice on display and test them out to get a feel of what you like. Nothing I do or say can change a personal preference and style.
As for monitor, stick with Samsung, Asus, and Dell and you should be good. As was mentioned, less response (*MS) is good, but preferably you want 1080p or better in the size you want. Some people like 27", others like 21". I tend to stick around 23/24 myself.