Calculating monthly profit

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I am looking inot buying duplxes in my area for 115-150k.
I am trying to figure out what kind of positive cash flow they will create with zero down and the current monthly rental rates.

Example:
120k with 0 down
2800 a year in property tax
1800 in gross monthly rent
180 a month for proerty manager

How do I figure mortgage ins.?
Home ins?
and what else should I calculate?
Thanks