I would say the number is infinite. Zoey was gifted with all natural elements at once, same with Other Kevin. I don’t see why other fledglings would be limited in how many affinities they could possess (natural or other (horse affinity, poetry, music, etc.)).
I would say yes, in theory, but that fledgling would have to be even more important than Zoey Redbird, imo. I don’t think Nyx sees a reason to gift a fledgling with that many gifts/affinities, unless it were an apocalyptic-situation.