Not much to say here except measure everything out in advance and watch your temperatures. Don’t worry if your egg whites finish a little early, better they sit and get a little watery than your syrup cool to the point of setting. You can always whip the whites back up some before you start to pour the syrup into the mixer. Also, don’t be shy about letting the marshmallow fluff whip until it’s cold. It takes at least an hour to set at room temperature, so ten or fifteen minutes of whipping won’t do it any harm. You’ll get extra volume in the bargain. Ooops, I spilled some. Dang.