I brewed a Belgian with star anise last year. It is extremely powerful. If memory serves, I used just one or two "arm" per gallon, and club members still complained that it overpowered the beer. One whole star should be plenty for 5 gallons. Don't use any more than that. And in a weissbier, I would use even less, about half of a star, just to add a little something interesting in the background and not overpower everything else.