regarding your first point, turn off instant 2D.
1. That's "Instant 2d". There are several discussions here about it. A search should turn them up.
2. You should get a dialog box show up if there are components that can't be found, asking what you want to do. Check your dismissed messages to see if it's there.
3. That terminology has changed to "User defined" in SW2017.
It's always a good idea to review the What's New document so you are familiar with what is new/different, or if you encounter something you don't like/aren't familiar with such as in these cases, search the What's New and regular documentation. Here are the topics specifically on these items:
3) I'm not familiar with exactly what you are referring to here, although maybe Glenn does since he already commented on it.
On the last one, the problem is that the menus are growing very large due to the amount of functionality added over the years and we had to consolidate things in the menus because the default menus no longer fit on many monitors (which causes Microsoft to put REALLY inefficient buttons for scrolling on the menus). For the most part, menus are supposed to be one of the last resorts for running commands since menus are probably the most inefficient UI to access them. Certainly, SOLIDWORKS didn't implement Microsoft menus as the way to make SOLIDWORKS more efficient than Pro/E; menus are just the "catch all" for where pretty much every command is located. If you use measure often, I would recommend you use one of the many more efficient ways to access commands such as toolbar buttons, keyboard shortcuts, mouse gestures, shortcut bar, context toolbar, etc.