You will not be able to chat in the actual games themselves (well you wouldn't be able to anyway unless you had 15 arms right?) but you will be able to create "lobbies" in which you can chat amongst your mates while you wait for other racers.
USB keyboard's are expected to be supported although you will still be able to use the tediously slow on screen keyboard.
It sounds like the Mario Kart Wii online experience is going to be fairly well polished but no doubt some people will still manage to complain. I'm not too concerned about the lack of voice chat and am pleased to hear that you'll be able to form "lobbies".
All is good in the world?