I'm playing an Orc and i want to do more around the strongholds, other than beating up the Chief and mining ore for coin. Are there major quests for any of them(ive only been to two)? And if there isnt any, why not?

There is at least one major one that I know of.

the one in Riften, there is a level requirment

You serve Malacath

The only other thing i know of is you can marry an Orc woman, Borgakh the Steel Heart, from Mor Khazgur