Reload time.

[PvK]

Can it target 10 with DF, and then more with seekers?

You could also put on some drones and fighters. During beta I ran a test of how many fighters would crash the program, and there didn't seem to be a limit. The zoom map looked pretty scary when almost the entire tactical map was filling with fighters spreading from planets (this was using the simulator and Proportions mod where there is plenty of room on planets).

PvK