Not sure I'd want all that in the living room.

I think you will have to move these around to see what looks best. You can try them behind the couch. You can try them on each side of the couch on the wall. You can try them on the walls near the entrance to the dining room....etc...

Yes but you can't style it with too much stuff and much of case is too low for photos or decor. If you put them on either side of the dining door, that wall will be a big busy fest.

Bookcases should be preferably in interior wall (not exterior) to avoid humidity. Besides bookcases should be in ventilated area, out of sun light, far away from water and humidity and If you plan to have open shelves it is better to place the bookcase out of dust but in ventilated area. Books are sensitive and don't tolerate humidity and sun exposure. The bookshelves should be placed far away from bed in areas of earthquake risk.

What if you painted them to match the wall color with a pretty coral backing or wall paper so that the empty areas were pretty and fun? You can also hang art on the front of the shelves, but not too low.

Love, love, love books. Your pale oak colour choice for your walls by Benjamin Moore is terrific! Keep the current trim white near the ceiling, floor and frame opening. Prime and paint out your bookshelves the same colour as your walls will be (Pale oak) and place them on either side of the frame opening so that they look like built-ins (be sure that they sit properly centered on the walls, on either side of the trim for that opening). They will be shorter in height, I think, than the framed opening. No matter. Get two identical, gorgeous, full and lush potted plants or two identical and cool rectangular baskets to place on either shelf to lift the eye upward and extend the height of the shelves. Find some french doors painted the same white as your trim, that open into the dining area. You can have some impact here by having a spectacular colour in that dining room to contrast with the pale living room, just be sure that the colour is complementary to Pale Oak by Benjamin Moore. If your current dining colour does not complement Pale Oak, change it to one that does (perhaps something with a colour be it pale or dark that grabs the eye's attention rather than just a neutral). The transition from one room to the next will be beautiful!

My two cents worth.

Have we seen all 4 walls of the living room? How would we know the best location for them without context?

It is possible they'd do better separated and used in different rooms.

If you do this, I would paint the bookcases to match the trim. I'd also trim them out so they fit the space from door casing to wall exactly. Might need a carpenter to do that for you. As you can see, I didn't do any of that. But I would in real life.

If you are really going to paint them, then paint them white. If you don't like the white it will be your primer so that you can paint them another color.

Paint them to match your wood trim (white). You may want to consider using wallpaper for the backing. Grasscloth is a great choice for a background.

Center your bookshelves on their respective walls and go with bookshelves the same colour as your walls. Keep all of your trim in the space, the same white that you have surrounding the opening to the dining room for contrast. Because your shelves are filled with mostly books, you can keep paint the outside and inside of these shelves all of the same wall colour. Your books will add colour. If you do eventually go with french doors, keep them in the same colour as the white trim! When done, if you find the interior backs of the shelves too plain (doubt they will appear this way), you can always add a wallpaper or contrasting paint colour. Would love to see an after picture! You do also need a great looking area rug in your living room if you do not already have one! I would find this after doing the bookshelves but before changing the dining room colour if you go that route.

Last thing. Can't tell colour of your ceiling, but consider keeping it the same colour as the trim around the opening (white), the white it is now if it is OR paint our your ceiling your wall colour...a floating trick when you want the space to seem taller.