Workshop

Useless . To hell with probabilities. Better to have 100% protection once every 2-3 nights.

Same here. Better to give 2 Night Defenses: a regular kill (every night) and an anonymous one (once every 2-3 nights).

Then the city will simply have three defenders. But I can't think of an equivalent.

Regarding the second point - yes, you're probably right, that would be better. Better to do it every other night - that will be 50%, essentially.