Based on the sentences you gave, the sentences are all implying the same thing.
'Work' and 'Job' do mean the same thing. But it is better if you say job.
For 'Have' and 'Do', it would be best to say 'do' as it indicates that the graduates are in already having the job and are doing it.
Thus, the most natural answer would be number 2: The number of graduates that chose to do part-time jobs is 2000.