Configuration, chirality
Your drawing is correct and yes, "I read that I can simply assign a priority with the fourth priority group on a wedge and then take the opposite of whatever I assigned" this is true too.  In your drawing 1->2->3 is a clockwise rotation (therefore "R" but), but the lowest priority item (4) is coming out towards you.  Therefor, the R/S assignment needs to be reversed (from "R") to "S".