I live on the Island and have run this race a couple of time now. Hills, depend on your fitness. A couple are long and a few short sharp one. The killer one seems to be after you run along flat bembridge embankment. Then you hit the hill going into St helens.
As for the traffic. Mostly impatient holidayers trying to get to the ice cream van. I found the main road between Brading and sandown to be the worst but you can cross over at some point and usse the footpath.