Hi Fabrice,
The defaultproperties block doesn’t exist anymore, but everything that you would have done with it now lives in the C++ constructor for your class (e.g., AMyPawn::AMyPawn(const FPostConstructInitializeProperties& PCIP)).
In order to do a custom character animation, you would first create a Vim Blueprint in the editor, which is similar in concept to the AnimTree asset in UE3, but much more powerful as it can also contain arbitrary blueprint logic.
Once that is done, on your skeletal mesh component, fill out the AnimationBlueprint property to reference your vim asset.
There are two different schools of thought about content references in C++. You can either directly reference the vim in C++, doing something like the following in your constructor:
static ConstructorHelpers::FObjectFinder MyVim(TEXT("VimBlueprint'/Game/MyCharacterVim.MyCharacterVim'"));
MySkeletalMesh->AnimationBlueprint = MyVim.Object;
Or alternatively, leave it unassigned and treat the C++ class as a base class, creating a derived blueprint of your character/pawn, and filling out the AnimationBlueprint reference in the editor. This approach is a tiny bit more work initially, but is data driven and leaves the C++ code with a looser binding to content.
Cheers,
Michael Noland