Lavorare come [titolo professionale] is idiomatic = "to work as a [job title]". A dictionary with examples confirms this.
I have always thought that adding an article as in lavorare come un [...] turns it into the comparison "works like a [...]". Google Translate confirms this, but its source is bilingual texts of unknown accuracy, not scholars or natives.
This is all American, in English it is "Postman" I do not understand why Duolingo uses American terms like "Soccer" "Mailman" etc, they should use English words. Another time it showed me as mistake "Have you?" and its correct version is " Do you have?" Anyone who speak proper English will tell you that "Have you" is a perfectly acceptable way to ask the question.
We absolutely say "mail carrier" in the United States to include mail carries of both genders under one term. The terminology changed years ago. (It's no longer proper to say mailman.) It's the same reason we use police officer, fire fighter, etc, instead of the antiquated policeman, fireman.....
No, in English we always use personal pronouns. It's because there are so few different verb endings. For example 'work' is used with I, we, you (singular and plural) and they. So it is necessary always to say who is the subject of the verb. Sometimes it means we have to use the inconvenient phrase 'he or she' when we don't know the gender of the subject.