I have a question on 3/4" x 12" pine shelving. Span ranges from 6'-7', 3', and very long, maybe 12' shelves. How important is it to have a strip of wood (about an inch) placed across the front of the shelf. Also does it need to be permanently screwed down to the support strips running under them and along the sides? What about brackets? Some will be storing heavy items, other lightweight, but certainly items would change over time.