Once you get to a certain level in Counter Strike, you will likely begin to obsess over your mouse and config settings.
My advice for dealing with this difficult phase is to just buy a mouse you are comfortable with, that is good quality, and experiment with DPI / Sensitity settings for a while.
I personally use a Razer Deathadder at 500 DPI and my in game sensitivity is around 4. I also use a SteelSeries QcK mousemat. Before this setup I was using a really cheap optical mouse that had a set DPI of about 800, and I used this with no mouse mat and in game sensitivty of about 8. At first the difference between the two setups was horrific – I just couldnt understand why anyone would play with low DPI / Sensitivity settings. After a couple weeks though, I found the lower DPI let me be much more accurate. I’m still not sure about the size of the Deathadder, but Im not spending another £30+ on a mouse so I guess I am stuck with it.
If you do use a high DPI + Sens setup then I would recommend you try a lower setup for a couple of weeks, just to see if you might prefer it.
Regarding the rest of your hardware / peripherals:
Ideally you would have a PC that could run CSGO at a steady 120+ FPS. If you can afford a 120hz monitor then I would go for one of those too. You also want a decent set of headphones, and either a webcam mic, or a headset with a mic attached.