Your explanation is about right, Tony. The forms overlap, but 'meet with' suggests an extended, more formal discussion, while #1 and #3 indicate no more than getting together. '#3 suggests to me a quick getting together in order to do something else: 'We're meeting up in Rome and going on to Venice from there'.
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tinanam0102Person A: I'll meet you up at the subway at 8:30 am.The subway is not up, it's down.
tinanam0102 "I'll meet you down the subway"?Not quite: