Honestly I'm much more interested and curious about what the expectation is regarding the PC's lot in life and the sorts of adventures they are expected to go on. To me WFRP has always been a game about being a lowly Ratcatcher, Vagabond or Peasant who must make his way in a world where starvation, disease and an angry pig are very real threats to life and limb. Like literally someday somebody will ask you, "How'd you get the wooden leg?" and you'll say, "Well see, there was this pig..." To me, that very grim n gritty type of game is what I really enjoy most about the WFRP world and I'm hoping the tradition is continued in this edition.
I can't say very much about the tone of the game, since I played it only briefly and didn't look at the rules or fluff in very much detail at all.
However, Evan (the GM) did say that the game billed itself as a game of heroism, which did seem like a departure to me.
That said, there's a huge deck of critical wounds, another deck of insanities, one of magical backfires, and a fourth deck that I don't recall which I think also had some nastiness in it. Basic careers are fairly similar to the assortment available in 2e, though notably absent is the rat catcher (and by extension his small, but vicious, dog).
Character stats and abilities are tracked via cards instead of pen and paper (or an app).
No, you still have a character sheet which keeps track of all your stats.
The cards only track your talents and actions, sort of akin to D&D's feats and powers respectively.
The reason they're provided as cards is because you need to manipulate them in various ways as the state of the game changes. Some talents, for example, are always on, while others have to be expended when you use them. You can also lend your talents out to the entire group by moving them to the group sheet, which is basically a simplified character sheet giving the character of the group as a whole (things like Swords for Hire, Band of Thugs, etc). For actions, you need to flip them over to the correct side depending on your stance and need to place delay markers on them to keep track of how long before they can be used again.