It’s up to you to implement the method inside your own class, so implementation is left entirely up to you. This might cause a problem on a higher-level scale if similarly named methods from different interfaces expect different data, but as far as compiler cares you’re okay.

In an interface class, all methods are abstract - there is no implementation.  In an abstract class some methods can be concrete.  In an interface class, no accessibility modifiers are allowed.  An abstract class may have accessibility modifiers.

Structs are value-type variables and are thus saved on the stack, additional overhead but faster retrieval.  Another difference is that structs cannot inherit.

Value.  The data type of the value parameter is defined by whatever data type the property is declared as.

The method or property can be overridden.

When overriding a method, you change the behavior of the method for the derived class.  Overloading a method simply involves having another method with the same name within the class.

No.  The signature of the virtual method must remain the same. 
  (Note: Only the keyword virtual is changed to keyword override)

Different parameter data types, different number of parameters, different order of parameters.

Yes, just place a colon, and then keyword base (parameter list to invoke the appropriate constructor) in the overloaded constructor definition inside the inherited class.