The salt won't hurt as long as you don't add too much. I think the general consensus is 1 tablespoon per 10 gallons. However, I wouldn't add salt unless my fish were sick. It's not necessary for your fish at this time, and would just be something extra in the tank. Also, goldfish prefer cooler water and are not considered tropical fish, and the angels are tropical fish. Do you have room for another tank? I think your goldies would be happier in an unheated tank, and the angels can get quite aggressive if they become a pair and spawn. I can't think of another more perfect excuse to feed your MTS (Multiple Tank Syndrome) than this one! ;D
I don't know about the common salt. It depends what that means. I use kosher salt. The fish vet I talked to said table salt shouldn't be used, but maybe that isn't what your pet store vendor was suggesting. I agree with Butterfly. The only time I have used salt on ly fish was when they were sick or had skin lesions.
Welcome to the hobby and the Group. I don't think I have had a chance to post to you yet.