Questions for Vigilant Trait

If you are not using the Arcean tech tree. What is the base amount the Vigilant starbase trait slows down enemy ships?

I can't see it in action. Does it get shown in enemy ships stats when you hover over them?

Also do multiple starbase overlapping add this effect in a cumulative manner?

Finally the base amount this traits adds to weapons of ships is +1

Is it cumulative if multiple starbases overlap?
Can you upgrade that number without the Arcean tech tree with a module or any other way?

Finally does the Vigilant Starbase trait impact shipyards? If so, how?

The documentation is sparse on these details.