Creating an abstract class(interface)

Thanks for your answer. Please shine some light on these questions regarding your above quote:

If I can create a ICollectible_Interface and inherit from it, AND cast to it, then how is this different from an abstract base? I mean, if I can use C++ syntax, why resort to UE4’s syntax?
Can I inherit a class from multiple Interfaces too(it wouldn’t be too useful if that wouldn’t be possible)? The documentation didn’t say too much on this, but can I also add data to an Interface?