Heather is fairly delicate in flavor. It does have it's own bittering properties as well though. When I brew my heather ale I use only heather, no hops. Sometimes bog myrtle if I can get it. I am looking to use meadowsweet in the future.
1-2 cups sounds like a good place to start. How many ibu's does this recipe have? When are the additions?
Fresh heather is infinitely better than dried. Watch out with buying dried heather too because you have no idea how long it has been sitting around. It is not a major mover as far as ingredients and as with all dried herbs it has a shelf life flavor and aroma wise.
Adding the heather in the last few minutes or at flamemout is best for flavor and aroma. You can add some at the beginning for bittering as well.
Here is another tip. If you ever plan on trying to "dry hop" (herb?) with heather in a light session ale be prepared to have a wild sour beer in the end.