To handle the Save or SaveAs commands, you can add these lines to your module:
Private Sub Workbook_BeforeSave(ByVal SaveAsUI As Boolean, Cancel As Boolean)
. . .
End Sub
To cancel the operation, execute ‘Cancel = True’.
I think that you can let the user to freely use New and Open operations to work with any other workbooks. Blocking Excel globally looks too severe.
But maybe the protection features of Excel can be used too. See the “Protect” group of “Review” tab.