how many regiments are you playing with? jow many do you think are suitable for organized play?

The recommended 2 from the rulebook. I expect this will be the tournament standard since you can play in around an hour. I have been wanting to try 3 regiments though, think the list building is more interesting at that level.

We've been playing with two, which I think will probably be the standard because of the speed of play.

We have played with one, two and three regiments:
One regiment is not really worth setting up, but a nice way to showcase the game if you do not want the tutorial from the rules.
Two regiments ist the bread and butter of this game and will probably be it's standard.
Three regiments is probably the most intense experience, but the game takes quite a while longer. If you have got the time, i encourage you to try it out!

are you guys running one hero per regiment or are you still only running one hero and then running multiples of that hero's build total? For some reason this wasn't clear to me.

It's one hero per regiment. 2 regiments will have two different heroes. 3 regiments will use three different heroes.

are you guys running one hero per regiment or are you still only running one hero and then running multiples of that hero's build total? For some reason this wasn't clear to me.

I am not sure i understand your question!

You first agree on the number of regiments.

You then choose that number of distinct heroes from either Order or Destruction.

You then buy a regiment for each of these heroes from that heroes' race and points.

I hope that clears it up a bit!