[Suicide Junkie]

You need the limit to be at least 50.
The mines will be fairly small and should be able to take chunks out of most of the ships in a fleet. When each mine hits a random ship, you should end up with a gaussian distribution, so most ships will have some damage, a few will be untouched, and a few will be severely hit or destroyed.

1) There should be more mines than ships unless the defender was surprised, or isn't relying much on mines.
2) The damage of a single mine should be small enough that a typical warship can shrug it off. 10 or 20 kt worth of armor with stock settings for everything else, perhaps. Adjust up or down depending on overall weapons damage / defenses strength in specific mod.