I have about 2000 ebooks in my files right now, the majority of which are classics. I like to keep those because the majority of what I read are classics. I have them somewhat organized into Calibre although I just found out about plug-ins which I think will be even better for organizing. I DON"T accumulate lots of freebies. Just because it's free doesn't mean I want it. I only download freebies that I might want to read later. For example, I don't download any suspense freebies because I won't ever read them.
I think as long as you can still find the books you want and you are not spending hours trying to find it, you can't have too many ebooks!