There's gonna be a few questions here, I'll try to keep them as clear as possible
Will there be any explanations IC as to why the Makani are suddenly capable of taking flight, or should we simply say "they always have" or make some excuse for each character, such as "they've recently learned how to utilize their wings better" / "they've grown stronger"? Is this an abrupt change to them, or could Makani fly in Vata'inu as well?
Are the Makani able to idle in the air, meaning, can they swish their wings hard and fast enough for them to basically float in one spot, bobbing in place and what not? Seeing it's like a pull-up to gain altitude, would it feel much the same to do this?
Also for clarification, I assume that the previous rule of "no using bows while gliding because it is too unsteady" carries over to flying too? What about the previously mentioned idling?
Vata'inu allowed for natural updrafts of warm air surrounding the island, and free flight was hardly a necessity. Perhaps it is safe to say that the strongest, most athletic of idols could have always flown freely, but advertised it as some taboo process. Why strain your delicate body when the island gives the only flight you will ever need? Then, the great disaster struck, and the world below changed all of that. Now, free flight is a tremendous advantage, and a Makani would be foolish to not temper and train themselves to do it, should the need arise. Depending on the character, it can indeed be that they have only just now managed to train their wings to carry them, or perhaps the more fit Makani have finally let go of that supposed taboo.
Idling in the air is possible, but it would still feel just the same, like they're doing pull-ups. It's not ideal to remain doing that unless you really have to, for some Reason. There is a lot of bobbing up and down, and they need to keep their body aligned properly so they do not lose altitude. For this reason, bows are a no-go, considering their need for proper body posture and arm pull for any significant form of accuracy. You could use a crossbow, but then you've got only one shot, and you can't reload in the air. Thrown weapons are your way to go, here.
Here’s a question about taking off, it says that spiritblessed of air can take off in 2 emotes. Would a potion of leaping have any effect on the take off? Make it go faster due to them able to gain slightly more altitude with it or not really?
For the sake of consistency in the flight rules, no.