Sounds like a typical molt to me too. The white powdery substance is probably the keratin coming off from around the new feathers. I had a good site on molting bookmarked on old comp, hold on and I'll find it. Ok, this is about cockatiels, but it's the same with keetshttp://www.cockatielcottage.net/molting.html
Like illusive said-a good molting supplement will help Usually comes in a can and doesn't cost much, Also bathing or misting helps with itchiness due to molting.
And yep, they lose tailfeathers too. As a matter of fact, over the past few days Ziggy has lost 2 of his longest tail feathers. He is now a stubby butt! LOL