No, you can enter a dragon, but it just counts down until you can release it. When the timer runs out, you can tap it to see what you won.
NO
Yes, it sells for $25,000.
The Colosseum in Dragonvale can be purchased upon reaching Level 10 for 50,000 coins. It takes four (4) hours to build.
Buy more or win them at the Colosseum.
You have to win events at the Colosseum or by crystals.You can get more by winning Gold and Silver (not sure if bronze) medals in the Colosseum.
You get 5 gems for winning
to get gems for free use the colosseum or try to get your friends on dragonvale to send you one free jem. If you want add me CSB_123.
you can win them when you get a silver medal or gold medal in the Colosseum, and in the dragon track
To answer your question, you will need to buy a Colosseum which costs about 50,000 coins in dragonvale. Other than that I don't think there are any other contests to come yet.
You get five gems for winning first place. You get 2 gems for winning second place. Select a dragon that is at least partially from the element the Colosseum is using that day.
the gladiators would fight to the death or fight animals
The Colosseum unlocks at level 10. It costs 50,000 coins.