Mutes are the most common, and in my opinion, one of best to start with. They are the classic swan that most people think of.
You would have to check with your state about regulations. Each state will have different requirements. Any native species- Trumpeters, Whistlers, etc would be covered under the Federal Waterfowl permit inorder to sell. Some states will require and additional endangered permit for Trumpeters.
Generally Blacks, Blacknecks, Coscorobas do not require permits.
Great if you have a pond or lake for them. But they can be raised in a pen with a rubber liner or cement pool. The key to success is being able to keep the water clean. With a pool that you can run water into that has a drain-- it is easy to keep clean.
Once swans are a few months old they are quite hardy. Our Mutes and Whoopers stay out on there ponds year round, as they have aerators to keep them open. Our others are moved into a barn for the winter once it gets really cold. It is not heated- just out of the wind- some pens have a small pool inside while a few only have a water dish.
We feed ours, shelled corn and duck grower pellets.
Randy