I am in the process of buying an Old 1 Room School House with an addition for my Home. The new addition has Old Barn Boards for siding running Vertically. There are some cracks between the boards, The person that put it up did not fill the cracks you can see the insulation board under it. What can I do to cover or fill the cracks Without making it to noticeable? The Old School part has Natural Cedar Siding on it. It is weathered, Not sure they did anything to it. Does it need to be treated? I am thinking about staining it. What should I do to prepare it before I stain it?

Thanks,
Scott