Report Of Data By Criteria

I have a large list of items (up to 3000) that are listed by category, description, part number and weight in columns C-F. Column A is where a user will enter a quantity in the rows of the items that they want. Once the user is done picking their items they hit a button that I have written a macro in, to copy and paste only the rows that contain a quantity in, on to another sheet. My problem is that for these items (that contain a quantity) I need to have a line number (in column B) that starts at 1 and counts up for each line item. Issues to consider:

-Line item 1 may not always be the top item. (because the user may not choose the top item)
-There will be spaces inbetween the line items since the user may not pick all of their chosen items in order.
-Users can pick an item at the bottom then pick one above it. (The Line item numbers will need to readjust to include the new number in the middle)

This has been bugging for a few days now cause whenever I think I finally get it I keep creating circular references