I don't agree with (1) at all. Scroll bars are more efficient because they allow you to immediately jump anywhere within the document. In fact even when using Windows 8 on a tablet I sometimes use a mouse or pen JUST so I can get the scrollbar and jump to the bottom of a document. For an easy way to scroll mousewheel or two-finger touchpad motions are far more pleasant. The mouse should not be used to imitate touch gestures! It should have its own input language that fits what it is good at. They made that mistake with the "drag screen up to unlock" which was thankfully fixed in RP. "Swiping" with a mouse is just an awkward, unnatural feeling motion.
Rather than yet another redundant way of scrolling I'd prefer that the "drag in empty area" with mouse be used for something else, such as quickly selecting multiple items with a rectangle as it is on desktop.
The problem with (3) is that once you've "used up" the edges of the screen by making them trigger the app bars, you can't use them for anything else - on horizontally scrolling canvases this would break the scrollbar and semantic zoom control for example. Personally I wonder if there shouldn't be a separate control for commanding with mouse (with the same commands), something like the transparent mini-toolbar in Office, that would allow you to command a selection without having to take your mouse pointer down to the bottom of the screen (and back up again).
For (4), I agree there need to be more keyboard shortcuts and I also have a related gripe which is that there's no way to easily learn/discover keyboard shortcuts in Metro style apps other than knowing them from desktop apps or trying every key on the keyboard. The app bars need to have something like underlines in menus, keytips in ribbons, etc., where you can hit a key like ALT and see the available keyboard shortcuts.