Some good suggestion so far ...
Your boards are too narrow for this project, based on the photo. You gave no width dimension or lengths, so it's hard to tell. Regardless, to get the widths you need, you'll have to glue them edge to edge and possibly butt join them... I donno? This will result in a patchwork of grains and patterns that in my opinion will not look good. Plywood would be a better choice, more stable, straight grain direction and no glue joints showing.
You can glue strips on the edges to cover the raw plywood. You can use a 1/4" plywood back, recessed in a rabbet and with 1/4" shorter shelves.
I would save this wood for smaller projects like keepsake boxes, jewelry boxes, a treasure chest, etc.
The answer to your question will only be as detailed and specific as the question is detailed and specific. Good questions also include a sketch or a photo that illustrates your issue. (:< D)