Starcraft – Which SC2 units can accidentally cause friendly fire

Starcraft 1 has a different psionic storm than Starcraft 2, so I'll only be answering Starcraft 2

It is 80 damage spread out over 4 seconds. Psionic storm is true damage and is not reduced by abilities or armor. Any unit caught under the storm (friendly or otherwise) will take 80 damage if it remains for the full duration. Its worth noting that Zerg units at full health will regenerate 1 HP when first hit. Storms do not stack. Any unit under a storm gains the storm effect. It is this effect which conveys the damage. You can only have 1 storm effect at a time on a given unit.

Depending on your army composition running through storms is often recommended you run from storms. Because there is a slight animation delay (1.5 seconds) you can negate a large portion of the damage if you act quickly.

Storms only hurt units. Units inside bunkers or carriers or other transport are unaffected.

Storms have a range of 8.25 to 9.75 as they have a radius of 1.5. Smart cast means the closest templar will energy will cast the storm.

I believe you're talking about the Mercenary building. As you surmised, the # displayed indicates how many more times you can hire that band of mercs.

It resets every map.