Buy the game.

So, does the deluxe edition include everything?

No, it doesn't include the bonuses you get for pre-ordering.

Basically, is there a way to get all the possible extras without buying the original game five times?

No, you'll have to spend some money.

And what happens if, say, you activate the deluxe version on top of the current game?

I did that. I activated the collector's edition and the pre-order version on top of my base version. The result: additional content was unlocked (5 heroes, 3 dynasty weapons, 1 map). I don't regret the purchase at all. But I don't see the point in buying the gold edition just for the exclusive map.