There is a listing of every hero a nation gets in Edi's database on the army list page. Hero's are identified as heroes and multihero. The heros are unique, the multiheroes are not unique.
So your questios answers are:
1. refer to database.
2. refer to data base
3. refer to data base
4. yes. I have never seen two heroes appear in the same turn, but I cannot say it is impossible.
5. Yes. No heroes appear with negative luck. I don't know the actual probabilities thru luck 1,2,3.
6. Yes
