I would recommend looking at some home dec workroom sites for idea. That large a worktable is more along the lines of their setups. Try
workroomtech.com and look at some of their articles, like
this one
Be aware, without support (similar to having floor joists), if there is too much gap spanned between the bookcases the plywood will sag and bounce. It is not a rigid item, especially with a long, unsupported span. You need to fabricate something to support the plywood.
this is the worktable of my dreams!!! If only I had a space big enough for it.
Rob