Best for claw grip is long thin mouses as Razer DeathAdder, Roccat kova or budget versions as Sharkoon fireglider.
1) It depends on your budget for gaming mouse
2) Are you sure you are using claw grip, Difference betwean claw grip and fingertip grip is Does end of your palm touch mouse? If yes you are using clawgrip if no you are fingertip grip. and there is mouse difference.
3) For CS:GO i think is best to use (If you use right hand) 2 extra buttons on left side and 1 on right. (I use them for flash, HE 2 left and 1 right for talk.)
I am using fingertip grip and Sharkoon Drakonia. It has 2 top left buttons for HE and Flash, lower left for smoke and top right for talk. I know it is way to big for fingertip grip but is my old lovely...