Roughly an arm’s length of personal space is generally acceptable during conversations. With friends or family it may be less.
With business colleagues an arm’s length would be a minimum requirement, any closer could be deemed inappropriate, especially between colleagues of the opposite sex.
Touching is generally kept to a minimum during conversations. Between friends and family, light touching to emphasize a point or show closeness is more common. As a general rule, shoulders, upper-arms and elbows are considered safe non sexual touching zones