The YO will leave a hole, like lace, so that may not be what you want in a hat. If you do, yes it's worked over 4 sts and the YOs would stack over each other.
Most hats are kX sts, k2tog all the way around. Usually you work a plain round between the dec rounds, then each dec round is one less knit st between k2togs. When you get down to aobut 3 or 4 sts between decs, then you'd do that on every round.