Since you want to produce documents (notebooks and notes) I would use a doucment format for storage, that allows for light and shallow relations: XML with XQuery on the backend (eXistDB or BaseX, I can recommend BaseX). REST and websockets are a welcome addition, these XML database/XQuery processors can satisfy. They can convert to many JSON formats, which then you may consume on the client side.
As for the client side: I tend not to think about that too much, since it is often quicker and easier to create your own DOM manipulation than learning any of these, highly opinionated, frameworks. I like to use jQuery, because of the huge community, the large number of plugins and since many other frameworks try to stay compatible.
As for the client side: I tend not to think about that too much, since it is often quicker and easier to create your own DOM manipulation than learning any of these, highly opinionated, frameworks. I like to use jQuery, because of the huge community, the large number of plugins and since many other frameworks try to stay compatible.