Here's some more info about the Orcs, though I don't remember the exact source...

1) The order of Stronghold units by level:
Level 1 - Goblins.
Level 2 - Centaurs. They shoot.
Level 3 - Orcish Warriors.
Level 4 - Orcish Shamans.
Level 5 - Orcish Chieftains.
Level 6 - Wyverns.
Level 7 - Tamed Cyclops.

2) The city has several unique buildings - one allows you to exchange creatures for resources; another provides a bonus to Rage at the beginning of each battle; nothing is known about the effects of the others yet.

3) Orcs will have travel magic, but not combat magic. How it will be implemented is unknown.