Paul,
Both good questions for someone new to Inspire (Or anyone)- it's always nice to see people trying new things with the software. I'll try to assist but one of our users may also have solutions or ideas.
I don't think it's possible to have any particular action trigger based on an object's position relative to another object, except using containers, and even then the action would be limited to having a sound play (Which may depending on circumstances have the same effect as a correct box- that is, if sound is a possibility, then someone applauding).
I can say with certainty that it's not possible to have multiple actions on one object.
Unfortunately, you cannot have an object move along a path other than along its center. Your solution of making a second, invisible line by cloning the first and making it transparent is probably the best, though you may also be able to group your object with an invisible object so that the center of the grouped object is the top of the visible object. One might think to use the snap points for this but I checked and unless I'm missing something they don't work for movement restrictions along a path.
Again, all good questions and I'd be happy to raise as enhancement requests (Though I'm not sure whether it will be possible to implement all or any). I've logged this against case number 253901, please let us know if we can assist further. Thank you,