"Die Leute essen Nudeln mit Hähnchen."
Translation:The people eat pasta with chicken.
Menschen is a very general term, apart from 'people' it can even mean 'humans'. Leute is rather informal, since it translates to 'people, folks, gentry, peeps'. Personen is more formal than Leute. Hope this makes it any clearer for you.
Not really, "people" would be seen as a group of humans in the mass rather than as distinct individuals, as in "I know a lot of people" or "an unknown number of people". If you wanted to distinguish individuals then you would probably use person or persons as in "the crime was committed by a person, or persons, unknown"