So, basically I want various new powerups similiar to the ones in sc1. I want them to be pick-up-able with a SCV and detectable via a trigger, that's pretty much it
So, what's the best way to do so?

First, you'll need to decide on the models for them. You can attach them to the SCV's using "Attach actor to actor" (or something like that) action. Try something like "An order is issued" for event and "unit-type of target of issued order is "unit powerup"" for condition (well, something like that). Basically, when the SCV is near the powerup, the powerup will disappear and the actor will attach to the hand or something similar of the SCV (choose the correct attachment point). To detect that the powerup is there, check for an actor-attachment checking condition, and if that doesn't exist, make it so that the unit is given a dummy behavior/ability to signify that it's holding the powerup. For example, dummy behavior x (which does nothing) would mean that powerup x is being held, while dummy behavior z would mean that powerup z is being held.