Oh boy, that does not sound fun but it's probably better to drive with pets than fly these days. 

The niche bending was abused in LoK I felt, it really diminished the impact of someone bending something so small or difficult. I will say the metal bending was cool but other than that it seemed like suddenly everyone could bend in LoK and it made it less special in my mind. And adding stones and even maybe thin wood cuffs would be a great idea. I think it's a great way for benders to show some individuality. Maybe on one hand they have one fabric on and the other, something different to offer different styles of bending. 

What about the era? Something akin to ALTA, LoK? The mid 90s like Harry Potter? Something modern but vague in location? Or something more rustic? I think the ages are good and mature situations will need to happen with those who are of age, I agree. 

We could go the cheesy route and say they all found some special marble or gem that boosts their bending maybe allowing them to create some new element? I do think the major conflict or prophecy could be as major or minor as we'd like. It just depends if we want to keep the stakes low or have them eventually escalate. 

In terms of elements you were thinking of, any idea which ones you'd like?

I'd probably like a male or female earth bender, I like the idea of them wearing a lace band around their neck and letting dirt fly out of their mouth at their enemy. XD I also see them conjuring boulders with their hands. I'd say in terms of using the elements, they don't need to be present to be used (like hot you needed water nearby to water bend).