In the past I've hardly ever had more than 50 books on any one ereader. Usually it's closer to 20 or 30 books. My current book will be there, along with a few books I think I might want to read very soon and maybe some books I want to look over a bit.
However when I got my Paperwhite 4 the only way I could get the 3G version was to get it with 32 gig and I've been experimenting since I have all that space. As I think of it I've been downloading more and more books to it. I currently have 140 books on it and I'm sure I'll have a lot more on it before I decide if I like doing this.
It does make browsing more difficult, not because it's slower. It's not. But just because there's so much more to browse through. In the past I'd always just page to the book I was looking for. Now I'm using search to find books. It takes forever to get to the book I want to look at. And that'll get worse as more books are added. I have well over 1,000 books in my Amazon library.
I'm not sure I'll keep doing this in the long run. It's easier just having a few books on board. But I'm going to play with it more. I paid for 32 gig and I'm entitled to use it.
Barry