My preference in that case is to create different subforms for the separate scenarios, then load the appropriate subform as required. The reason for that is that each option may have different fields, and trying to hide/display the correct fields at run time is not always foolproof.
Option 1: Have all subforms on the main form, toggle visibility
You build each subform with the required fields. Set each one to be exactly the same size, then layer them on top of each other.
When the user selects what they will be doing (Combo box with list options like Order Stock, Customer Request, Existing Project), you set the visibility of the desired form to Yes and the others to No.
Option 2: Load a blank form.
Again, user selects from the combo. At this point you change the Source Form for the blank to whichever form is required.
Option 1 is easier to set up. Option 2 gives better performance.
If instead you want to go with the one subform, combo pulling data from two or more tables, you can use a
Union query as the row source for the combo.
Denis