One thing to keep in mind is that it's easy to think you need to keep all similar habitats on a single island. You don't.
Another misconception is that you need a lot of terra and flame habitats. You don't. In fact you want to minimize those because they don't hold much gold. I have eliminated all of them except for the ones that are upgraded with tokens. Take a look at your dragons with the Terra element... all but two of them (Terra and Double Terra) also have another element. Any other habitat is a better home for that dragon.
As far as that goes, then, there's a tier of where you want to try to put your dragons. You want to put them in the habitats that hold the most gold because you're not in the game every 5 minutes collecting, right? Specifically, Flame, Terra, Sea, Nature aren't that great and you should store your excess of those and replace them with higher-gold-capacity habitats that can still hold your dragons.
Part of the reason you try to keep them together is because of the crystals. There are Flame crystals and Terra crystals for example, and you would think you want those by Terra and Flame habitats. You don't. You want those by Terra and Flame dragons in upgraded habitats that hold lots of gold. I happen to like Light and Dark habitats for that because there are a lot of dragons that are say Terra/Dark or Terra/Light that can sit there just fine and produce +20/40/60/80% gold for being near a crystal even though they are in the "wrong color" habitat.
When it comes to those specific elements, Terra and Flame, there are a whole lot of dragons that have both. Why not put them in the best upgraded habitats you can and surround them with BOTH the Terra and Flame crystals?
So see what I did here...on the upper left I have an Electric, Light, and two Dark habitats in a row. All of those have Flame dragons in them (Flame/Electric, Flame/Light, etc.) . In front of those are the four Flame habitats I still have, all of them upgraded and all of them with Flame/Terra dragons in them. I stuck all four of the crystals right there so they hit the back row to some extent as well as the next row in which is an Electric, two Terras and a Dark, all containing Terra/Flame dragons as well. Behind that I have another lonely Terra (upgraded it can hold 70K), then light and two darks that contain Terra/Light and Terra/Dark dragons.
I stuck the Dragon Market in the middle because I had a bit of waste space. I don't go out for decorations but there are some spaces around the edges here that you could put flowers or tiles or whatever.
If you want, I'll show you another of my islands and what I did to maximize it, but this is the general point.