I think it’s a great idea to store your BOS pages in plastic sleeves, @wendy4! 
And yes, when one binder is no longer enough- it sounds like it’s time to split it into multiple books! I know you’re not the only one to divy up with many binders, @roxanne has shared pictures of her lovely multiple Books too, in Time for a New Grimoire 
As for writing in a big font, I wonder if there is some way to increase the size of digital pages? If you have your pages typed in a word document, you could adjust the font size there. A bigger font will definitely make reading easier! 
There’s another discussion about Book of Shadows ideas and brainstorming in Book of Shadows Stuff. You may enjoy browsing through there for more ideas to help organize your BOS as you divide them into multiple binders! 
