Like I said in the other post, you cannot 
The only way you can talk to actors in a level, is to have the level actually loaded.
Also, it is possible to send information to the level BP ( of the loaded level ) in some circumstances, but it’s MUCH easier to put your level BP code in a BP actor in the level. Then you CAN talk to it easily from other actors.
You can always do a ‘get all actors of class with tag’, and tag the actor you want to talk to. Be aware that this is not a very efficient method though (since UE has to loop through all availalbe actors) so better to do it before game start and store the result somewhere.
Not when the actor is in an unloaded level 
Yes, yes… of course