You can think of each Stronghold Turn as being an extra reward for any full completion of a Quest (Main Quest, Side Quest, or Task), whenever a Quest is marked off as finished in the Quest Journal.
How to Have a Good Stronghold Experience
Since Stronghold events only occur on Stronghold Turns, it makes sense to try to avoid turning in Quests before acquiring your Stronghold. However, there are some Quests that are required in order to get the Stronghold itself.
Once you get the Stronghold, rationing Quest turn-in's allows you to save up Strongho