Update on the used games:

Yoshida reaffirmed that “disc-based games on PS4” will work on any other PlayStation 4. So, as first reported yesterday, PS4 will have no used games/shared games lock for retail, store-bought titles. -IGN

Also i found on a dutch gaming site (gamer.nl) which said that the PS4 does not have be connected with the internet at all times!

Could not find anything on backwards compatibility though..