You have to be patient and gradually build the game. I have only been playing for 2 weeks and I am on level 21. I have not bought any gems but by playing the coliseum and the race track I expect to get the EBI in the next few weeks. I have already upgraded the hatchery.
If you keep visiting the game you can collect the coins earned at each habitat. This soon builds up. When I have time I leave the game open and just keep tapping the habitats every few minutes. I also got a lot of coins, food and Xp from the race track while I was building Kairos. I am still playing the race track as it seems to work through the levels more quickly than breeding the dragons. I haven't yet achieved any of the major dragons talked about on this forum but it appears that you may have to breed dragons 50 times to get the eggs you want. It seems that some players have been playing for over a year.
Good luck