>Drone congregation areas. Are they static year after year?
If the lay of the land doesn't chance, yes. They follow tree rows and roads.
>If so, what makes a good DCA, and how do they find it?
At the intersection of two tree rows and by pheromones.
>How does the Q find it?
By the lay of the land and by pheromones.
> If the DCAs move year to year, it's even more mysterious, how do drones from multiple hives "decide" to congregate here?
They follow the tree rows and they pick an open space where two of those intersect.
> How do the virgin Qs get invited?
Pheromones and the obvious path they follow.