The Net Worth Calculator allows you to record information on your monthly assets and liabilities, and graph or display a data table of your net worth.
Yes, you can mark any asset or liability value as private if you do not want it to displayed.
No: asset or liability labels must be unique for a given month.
Yes, you can specify a specific month, eg [networth month="2009-09"]
Yes, this is the default behaviour if you add a graph or data table without including a "month" selection.
All data is stored within the database for your WordPress installation.