Point 2; if you have thoughtfully saved the local copy of the notebook as a package file (more compact, the default selection for Save As and an all-round Good Thing), you cannot use Open Notebook to open the package. Use Open Section and OneNote will unpack the package - and offer all the usual options for when you create a notebook, including saving it on the server as a mult-user notebook. All I need to do now is delete the now-out-of-date notebooks (as I'm not wearing the brave trousers and haven't unpacked the local notebooks over the top of the server notebooks).
This is why I'd like to see a OneNote note manager PowerToy that could let me walk the tree of notebooks, sections and pages and move things around without opening up the notebooks and sections and doing it by hand. Pages, sections and notebooks are like files and folders and I can move files without opening them in an application.