It feels like cheating a bit, but is there any reason not to travel back and forth or rest over and over to complete sections of the Stronghold that are currently being built, until the entire thing is finished? 

 

I'm pretty sure I read that some of the stronghold objectives are completed only by finishing quests?  In which case, I'd like to complete a good portion of the stronghold to ensure that I maximize those objectives, while I'm out questing. 

As far as I know, there isn't a good reason not to.  However, I'm not far enough to know if the attacks are scripted or random depending on security and prestige.