1. Yes, it is safe buying on line. It is advisable to to check out the sellers reputation. Normally the fish will be packaged to arrive alive and you can insure the shipment.
2. Damsels and Clowns are fairly hardy fish and many people have started out with them. Be sure to research the needs and care of them before you buy.
3. Marine fish are difficult to breed, so it is not likely you will be faced with a lot of eggs.