Of course 1 damsel is not aggreesive. Aggressive to what??? As my dad always said, it takes 2 to fight. Damsels ARE agressive. Fortunately some clowns are MORE agressive (e.g. Clarkii).
Yes, you can raise clowns. Many do and there's lots of info available on the 'net. But, hybrid clowns may lay eggs and they may never hatch. That is natures way to protect sub-species cross breeding. Just like how a donkey and a horse can be bred to creat a mule, most of the times mules CANNOT be bred. Sure, they'll go thru the motions but alas, nothing happens.
Many people try to breed clowns, not realizing they have hybrids and although the eggs are laid, they never hatch. The more "designer" the clowns are the more likely they are to be a hybrid clown.