The belt will probably last 100,000 miles but I understand we should actually change it around 70,000 to be safe. Don't want to get stuck on the road. A few rare cases a stone gets cought in the belt and shortens its life.
All the Yamaha bikes have very reliable engines. I don't have a Road star, some buddys do, I know of no problems. Its a bike that has been around for a while. You don't hear much about cruisers with high mileage. My guess it is a hundred k engine. Like most others.