Creating fields that are filled in sequence by selecting from a master list

I'm trying to create fields that are filled in sequence from an existing list of items that are selected by checkboxes.  I need an item to fill the first field in the colum, unless it already contains data, if so, I need it to use the next field, and so on.  I have a list of nearly 100 items that could potentially be selected.

I had limited success using an action builder in LiveCycle Designer and am able to duplicate data from the list into a form, but not to fill fields in sequence.  If I select items 1, 8, and 15 from the list, or any other combination of items, I need it to fill in fields 1, 2, 3, etc. on my form.  Hoping someone can help me with a JavaScript that would work for this.  I'm thinking that the fields would need to adjust if an item is unselected as well.  I am currently using checkboxes to trigger the items in the list.