alt Hacker NewsIt doesn't really act that way, as (1) it can't be accessed with keyboard shortcuts and (2) it's difficult to scan for the desired feature as it's a visual jumble of buttons and text. Oh, and it might not be visible! Sometimes features can only be found in pop-out dialogs.
Having used Office products for 30+, my most-used feature of the Ribbon is Search, because I don't have time to waste hunting through a poorly-organised heap.
To your (1), if you tap Alt all of the alt keys current available show up next to their associated buttons. (Top level menu). Hit the letter for where you want to go and it than will show you the next set of alt keys (available items on the ribbon itself). You can also use the arrows to move around the menus or tabs when in this mode. It isn't obvious but the ribbon, as office implemented it, is very keyboard accessible.