Your fire is extremely stacked, haha. As far as your healer concerns, you'd be fine sticking with Cleo to start out with- since she's a dark unit (and the dark/light weakness always favors the player), she'll never take worse than neutral damage. As you pick up more on element healers, you'll be able to start diversifying more.
You'll want to try to have at least one character on each element that can resist an ailment your others can't (for instance, wind enemies typically inflict either stun or sleep). For fire, Sarisse resists both ailments so she'll cover that. I'd probably just focus on your natural five stars there to start. That being said, Sinoa is a fantastic buffer and Xuan Zang has a great debuff that's especially useful in raids. Down the line you may want to consider building one of those, especially the latter.
You don't have many options for water, but thankfully you do have a few excellent characters there. Elisanne has a good party buff, Karina covers your stun immunity, and Orsem is super good in his own right.
You've got a great selection for wind. Addis provides bleed which is extremely strong- he'd be a fantastic addition. He also has freeze resistance. Beyond him, I'd just choose from among Ku Hai, Ranzal, Aeleen and Eleonora while avoiding stacking up on weapon types. All but Aeleen have bog res so you'll be covered there.
Albert and Annelie are both great and have you covered for poison res on light, so you'll probably want a character with curse res. I'd go with Yachiyo or Amane.
For dark, insta include Sazanka since she's great and has bleed. For now you'll have to use Norwin and Orion. They're both pretty good.
Overall, outside of the lack of on element healers I'd say you made out very well for yourself. If you end up wanting to do high dragon trials down the line, you should already have somebody viable for all of them (hopefully so for light and dark, but we'll have to see how those fights turn out to know for sure).
