72 dpi is a screen resolution
300/240 dpi is a print resolution.
neither has anything to do with physical size, it's actually how many pixels you get within that size.
That's the general rule.
Regarding your drawings - what do you mean size? Are your art boards planned in pixels or mm's? What do you do with them? Use them online or print them?

Export Resolution in Adobe Illustrator
In Visual Studio 2010, I have a windows forms application frmMain.cs with a ComboBox. From the form itself I can access its value with cmbxYear.SelectedValue. I also have a DataSet.xsd file to bind to an rdlc report to a TableAdapter to present view data. The TableAdapter has a SelectCommand that takes SQL code.  I need to get the value of cmbxYear.SelectedValue into the WHERE clause of the TableAdapter.
Does anyone know how I can access/pass the variable value from the form into the DataSet TableAdapter SelectCommand WHERE clause?  
