I think that the question "как дела?" originally was asking information about how someone's commercial affairs (or business) were (was) going and that later it developed into a standard polite greeting formula. In English, business is normally used in the singular, not like in French where one would ask "Comment vont les affaires?, au pluriel. Anyway, we can agree that дела is not a verb (at least there is no such verb form that I know of, but as I already said, my Russian is still very poor). PS How many more languages are you planning to study?
No, it is usually not about commercial affairs. Дела could mean anything that happened with the person recently and was important to him/her. Typical answers are "Отлично/Хорошо/Нормально/Неплохо/Ничего/Сойдёт" and then (depending on your relationships) some possible details may follow, e.g. about graduating the Univercity or something about recent travelling somewhere or some recent health problems, anything related to person's children, visited events etc. Of course if you are not good friends or you will usually here one-two words in response.
Как дела - lit. How's business; how are things; used like "how are you?" Как ты - lit. How are you; implies previously known information; has a meaning like "how are you holding up?" or "how's life treating you?" Similar to the English phrases, it can be used as "how are you" but still has those connotations.
This is my interpretation. If a native speaker could confirm, that'd be great.
I was watching a youtube video about Russian pronunciation and the native speaker said it is not really proper, and that it is a mistake most non-native speakers make, to use как ты. Is there truth behind that?