I don't think you will get much in the way of sweetness from the orange zest and coriander. More of an orangey oil note/flavor and some earthy spice from the coriander (based on what type you use). I think your recipe looks solid, and if you have brewed it before and it was not too sweet for you then I would leave it where it is. If anything you might want to consider backing off on the coriander a tad, but that is personal preference.