Here is a link to some basic book preservation best-practices just as a refresher. One of the really cool things about archivists and preservation specialists is that they want spread best practices as far and as wide as they can so if you want more specific information on anything its very likely available.

I've worked in archives with large book collections in the past and the polyester bags aren't really ever used for them. For damaged books with loose sheets archival boxes are preferred. I think the best way to preserve a book collection like yours is just the basics for books: storing like sizes on shelves, making sure the books on the shelf are not leaning but not super tightly packed either, keep it out of rooms that are really bright or really humid, make sure there's no inserts or fasteners, and don't handle them all that much.

If they are thick enough that they can support themselves, I don't know if the bag and board is necessary. But I also don't know if it would hurt. Though obviously bagging and separating anything that is already moldy/mildewy is appropriate.

Unfortunately that kind of mass market 1950s-1980s are some of the hardest to preserve, particularly because they started using really high acid paper so the paper just gets more and more fragile until it falls apart.