Crowds lighten up at the end of August and predictions I've seen for your dates are crowd levels of 4-6 (pretty good), with the lightest crowds at the end of your stay. I'd personally just stay in your lovely offsite condo resort the whole time and be sure to hit the new HP stuff at Universal at rope drop vs. later in the day (should be better then than when more people arrive and you should be pretty good even though onsite guests will in all likelihood have early entrance). Like other posters have said, if the crowds seem like they are too much and you want an express pass, you could book a room for another night and / or buy express passes. I don't think you'll need them.