There is no diamond reward for the number of cups played in tribal conflict, and there is no world First, only a one-time corresponding gem reward in the achievement bar. The rewards are as follows:
Reaching 1 silver, or 1,250 cups, rewards you with 500 gems
Reach the crystal cup, which is 2000 cups, and reward 250 gems
Reach the Masters Cup, which is 2600 cups, and reward 1000 gems
Reach the Cup of Champions, which is 3,200 cups, with 2,000 gems