If I want to say his kindness is a huge impact on me, is it idiomatic to say so?Don't rely on one source when you are trying to understand the meaning of some word. "Affect" is neutral. You can affect things positively or negatively.
If you just mean to say that you like the guy, then you probably don't need "affect" at all: He's nice/kind, so I want to learn from him.
This is really a different perspective for us, because in Chinese culture we are less confident than the Westerners to describe or say something. Now I know that exaggeration are irritating at times and I will pay attention to it and think carefully then write or speak.If this kindness of his truly has a "huge impact" on you, you can say that.
I have to tell you, Sun, that many English-speakers tend to mistrust exaggerated statements about feelings. Understatement is not a crime when you want to say something complimentary about somebody: He's really kind, so I want to learn from him.
I often associate effusive language with insincerity or childish enthusiasm. I've heard too many speakers talk about how "awesome" ordinary things were, so this sort of chatter usually sounds ridiculous to me. If you told me that this person's kindness had a "huge impact" on you, I'd expect some convincing details about this huge impact. If you couldn't provide them, I'd think that you were using dramatic, insincere language about somebody's qualities.