Consider making boiling a small volume with those ingredients to make something of a tea. That helps with sanititation. You can also sample the tea to see if you think you have it powerful enough (or too powerful). You can add some or all of that tea to the secondary.
Also, keep in mind that that coriander often tastes and smells more like orange than the orange peel. It is potent stuff. Be careful, too, to get bitter orange peel, as opposed to sweet orange peel. I know a couple guys who added sweet orange peel, and their beers ended up with an unpleasant, hammy taste.
If you want to get the cheapest, highest quality coriander, check out an Indian grocery.