As I see, you are using spritebuilder, so you are using the new version of Cocos2D. In this version you can track a collision between two types of nodes. In your case, the coins and the hero.
This is as simple as:
1) Set your coin.physicsBody.collisionType = @"coin";
2) Set your hero.physicsBody.collisionType = @"hero";
3) Implement this method:
-(void)ccPhysicsCollisionPostSolve:(CCPhysicsCollisionPair *)pair hero:(CCNode *)nodeA coin:(CCNode *)nodeB{
//this method will be automatically called when the hero hits a coin.
//now call your method to remove the coin and call the method to add another coin.
}
To keep a count of the score, just make an int variable, int score;
. In your didLoadFromCCB method, initialize it to 0, score=0;
and inside this collision method, just do score++;
and maybe do a NSLog(@"Your score:%i",score);
Hope this helps.