A well-organized system derived from binder clips works for small/medium scale collections of debound books. It's a quick and easy, and relatively cheap, way to "rebind" them in parts. The clips even provide good surfaces for labels.

Archivists recommend standard ambient conditions or a little drier for long term storage. As you've said, too dry and the pages fall apart; permanent damage.

I suppose the fancy silica gels that maintain specific humidities would work in bags.