I'm very fond of
Ada.
My daughter,
Adelaide, goes by
Ada from time to time, so I picture a spunky little girl, full of life, very creative.
I've never met an
Ada, though I can see it catching on.
As for nns, it is a nn itself, so I don't think it needs one. I'd prefer
Ada as a nn for a longer name, like
Adelaide,
Adelle,
Adeline.