...not really. What happens when some insidious Empire card effect moves a hero from my battlefield into another one of my zones which already has another hero in it? I'm assuming one of those heroes must be discarded but is it the new entering hero, the one which was already there, either one - I choose, or either one Empire player chooses?

Neither. You cannot move a Hero into a zone where there already is one.

Now, I know that I can't legally play or move a hero into a zone that I already have a hero in, but just to be clear, are you saying that an opponent couldn't Forced March one of my heroes into one of my zones that already has a hero in it?

Yes. From the FAQ:

“Limit one Hero per zone”
If a player has a copy of a Hero in play, he
cannot play, take control of, move, or put
into play (via a card effect) another Hero
into that zone. His opponent also cannot
play, give control of, move, or put into
play (via a card effect) another Hero into
that zone.

What about an effect that flips up a development like Rip der 'eads Off? If the flipped development happens to be a hero in the same zone as another hero or a unique card that is already in play somewhere on my capital board, is the flipped card instantly sacrificed or is it something else?

Yes. You can flip a development faceup even if it is another copy of a Hero already in that zone, because you're not doing any of the things mentioned in that FAQ entry (turning a development faceup isn't putting the unit into or play, etc.). But you end up with an illegal game state, two heroes in the same zone, so the one that caused it - the second Hero to show up in the zone - is immediately sacrificed. Usually that's the one that got flipped up, but if for example you play a Hero into a zone and in response your opponent uses Rip on a development in the zone that's a Hero unit, that Hero will be there first and the one you played from hand will be sacrificed when it enters play.

I appreciate you taking the time to explain this so succinctly to me. I get it now.