You simply just have to buy or breed all hybrid dragons and regular ones :)
You can't win in dragonvale, unless you consider collecting all the dragons a win.
No dragons
All DragonVale hybrids are bred by picking two dragons of different elements to be bred with each other.
You either breed them or buy them with coins and gems
There's over 1,000 types it's almost impossible to know them all!
No they are not.
No, DragonVale dragons are not able to be traded.
No, emerald dragons are not breedable with any dragon. This is true of all of the birthstone dragons.
You feed them dragon food.
level 10
The dragons in DragonVale are not trainable. You only feed them to level them up and breed them.
All dragons are full adults at level 7