I don't know the proper terminology for onenote but assuming you can tag notes/pages: have a note for each resource where the note title is the resource title. Then tag the note with subject (however specific e.g. physics or solar_system or egypt or whatever), and also tag it with each of the years the resource is appropriate for (e.g. grade3 grade4 grade5). The body of the note would have anything specific to that resource such as lesson plans you've found for it, areas the resource is weak in that you might want to supplement, who recommended the resource, where it is (on your bookshelf, library, ebook on your computer, where to buy it etc) or why you saved it in the first place.
When you go to plan, you can search by tags for the subject and grade that you want.
One thing that might be tricky is managing the subject tags. I think you would probably want hierarchical tags, or tags to be tagged with other tags e.g. physics and chemistry be tagged with science so that when you search for science you can easily pull up all the subcategories as well.
I personally prefer subjects being the top level of organisation rather than grades as you mentioned in your original post since many resources work for multiple grades. But tagging with subject and grade independently means you don't need to decide.