correct, you need to test your calcium levels first and then add when needed. I dose everyday.
As for the live rock, the damsels could die if the rock causes an ammonia spike. But, many people have them during their cylce, so its your choice-- just a moral issue. Or you can take the fish back, buy the live rock and let it cycle. The rock should cycle the tank just fine, and if not you can throw a few raw shrimp in to kick start the cycle.
HTH,
Mark