Not sure if this is doable, but...

[Annie-nee]

Well, regarding that last, great -- you're already miles ahead of that one guy.

As for the Haibane...  The question you should really decide for purposes of the setting is if the Haibane are some manner of Celestial being, or just look like it.  This is important because the Celestials will certainly know if the Haibane are or not, and that will inevitably affect their interactions.  Now, you don't need to ever explicitly say what you've decided in a story, but you -- and eventually the rest of the writing team -- will need to know.  Just because you know, though, that doesn't mean the Haibane themselves will know, if you don't want them to.

And if they're Celestial, just because they look like Abrahamic angels doesn't mean they are.  No doubt you've already noticed that we don't align with any particular pantheon, either -- they all exist together.  And the Abrahamic religions aren't the only ones that used winged humanoids in their iconography.  Also, "little golden rings floating overhead" haloes are a degenerate representation of more general "divine glows" originating from the head or entire bodies of holy figures; they're not specifically Abrahamic, either.  Although we have one character, an Abrahamic Celestial, who has a visible halo at all times (check out Josh, if you haven't come across him yet), that doesn't mean anything as far as the Haibane are concerned.

They just look like angels.  No Celestial powers, special abilities, none of that.

I'm trying to remember where, exactly, but Yoshitoshi ABe said that he needed a way to make the Haibane visually distinct from the humans, and he went with itty-bitty wings and halos solely because they look cute.

Sure, they're born from cocoons, fully-grown, knowing how to walk, talk, basic life skills, etc., and they have about 8 or so years from hatching to Day of Flight but beyond all of that, they're humans with cute appendages.  They even get the flu.

The way I'd write them:

They've already taken their respective Flights, and emerge from cocoons in our world, days apart (despite their Flights not necessarily taking place at the same time in the show -- we only see 2, with one more implied to be in the "very near future").  The twist being that, unlike the amnesia when they hatch in the anime, here they'd remember their time in Glie (the name of the walled city in the anime).  The cocoons would be in 5 different rooms in a boarding house under renovation (in keeping with the Haibane hatching in places the humans aren't in).