This question doesn't have a straightforward answer. There are several good libraries out there -- not just jQuery, but also YUI, Closure, Dojo, ExtJS, and others -- and I don't think any of them have the same "shell".
My advice is, before you start thinking about the underlying implementation, first start thinking about the API. Start writing code that uses your library as if it were already fully formed, because that's going to help you figure out how you want it to work.
Once you've defined how you want it to work, then we can talk about how to implement that API.