I would survey existing libraries for other JSON document databases (MongoDB, Google's Firestore etc.) and steal all their best ideas.
But honestly, good API design is something that needs a lot of time to reach the polished state.
Whatever I can come with today, I'm sure a year from now I would find ways to improve that.
That has been my experience with much smaller libraries I wrote.
The more time you get to spend thinking about the problem, the better solution you can come up with.
I would survey existing libraries for other JSON document databases (MongoDB, Google's Firestore etc.) and steal all their best ideas.
But honestly, good API design is something that needs a lot of time to reach the polished state.
Whatever I can come with today, I'm sure a year from now I would find ways to improve that.
That has been my experience with much smaller libraries I wrote.
The more time you get to spend thinking about the problem, the better solution you can come up with.