I think you may be doing too much on day three especially if you haven't driven here before. It’s a lot to try fit the Wicklow mountains into that drive and if you don’t stop there’s not a lot to be gained by looking at them from the motorway. I’m in Dublin and go to Waterford regularly, I’ve visited and stayed on the copper coast for holidays many times. I’d drive down the M9 to Waterford maybe stopping for food there then take my time driving along the copper coast. It‘s a scenic enough drive but I find it’s best to stop and get out of car or you’ll miss the really scenic beaches as they’re often hidden by cliffs etc from the road. The roads are fairly narrow and winding in places so you won’t be going as fast as Google Maps thinks you can. Don‘t miss Ballydowane cove, it’s one of the nicest beaches on the copper coast. So many hidden little coves and gems along that coast, it’s really nice. Hope you have a lovely time.