If you have the ability, rabbet the back edges of the sides to accept the back. The back can either be 1/4" , 1/2" and nailed on OR 3/4" thick and rabbeted for the center shelves.... a bit difficult to get all the dadoes in the correct place.
The more secure the back, the stronger the cabinet will be. You also should not "over span" the shelves, 32" being a rough maximum for 3/4" shelving.
Don't forget to allow different height for various size books. Do not make the shelf spacing all the same. I would use 2 "fixed" shelves in a cabinet that is 8 ft tall. I would dado the sides to accept both shelves.
If you use pin holes for the shelf supports, then all the hole must be the same distance from the bottom or the shelves wont sit level. A temple would be best for that and they make drilling guides with the distances already drilled in.
OR you can use separate panels of material in between the shelves as spacers. These will act as "faux rabbets" to support them. This is what I do on larger cabinets sometimes since all you do is cut the panels the height you need for the shelves and place them in.
For a cabinet without face f aces you will need a means to conceal the plywood edges... either thin strips of the same material or the iron on edging.
Reply back with your questions and or progress.