In terms of the page tree, I took a look around some other CMSs and I've come to a first conclusion.
I would like to have the page tree in a sidebar, but not all the time, because a clean Interface is key. I'm more for the option to blend it in like the offcanvas Concrete5 does. If we want to keep the mouseover menu, enough space is necessary, more than in the image below.
On the majority of the systems a click on the page name opens the page to edit. Even if it is a parent page. Drag and drop to move pages are just implemented and don't use a additional click. I like the approach of the neos backend there, a click opens the page to edit. Dragging a page just happens naturally. The accordion is activated with a specific icon, not by clicking on the page name.