Not much to go on to be honest. Naeff all we know for certain is that he was not as strong as Nynaeve (that's stated when Nynaeve and he are cleaning up. the bubble of evil in Tear just before she Heals his insanity). So I put his maximum level as a 5
Thinking about it, its a good choice. He matched Aviendha's work with the river in tGS, and she's level 11, So he'd have to be 6 levels up to be her equal in effect. So level 5 works.
You could equally well place him just below her. She was worried about the pace of his gaining strength, not that he equalled her. We just assumed he had to already be stronger because we thought the upper levels of Aes Sedai were comically weak. But we know now that is not true.
One other thing: I noticed you placed people like Neald, Flinn, and other men at tentatively level 19 as minimum because they can Travel. For men, though, minimum Traveling level would be level 13.