A third of the way there!!!

Raw Completion.
After dissembling the rough fitment completely, I noted on the pieces how they were oriented when assembled so reconstruction would be easy and fast. Then I marked the placement of the shelves and where the shelf pins would need to be installed. After applying wood glue to the joints, I put everything back together.

Shelves.
The shelves were a little rough to work with in the ways of fitment. I did cut some short - width wise, but I think they will be fine support-wise and those minute errors will be hidden once the piece is stained. I measured the diagonals and everything is perfectly square at 51 & 1/4".

Putty Up.
I later filled the screw holes with Elmer's Paintable / Stainable Wood Putty and a putty scraper. After a few hours of drying, I'll begin sanding either tonight or this weekend. The sanding will serve to After the sanding treatment, I'll rub it down with cheesecloth to remove the left over saw dust and putty and let it sit and begin this piece's twin. It's rather exciting as I am a third of the way through with this project. I need to get the materials for the other two sections, so it'll be another trip to the lumber yard for me.

Next.
I will wait for a weekend with better weather to apply the stain and finish. The stain will be a couple liberal coats of a dark walnut color. Once dried and applied the stain will be sealed in a couple coats of glossy clear coat.