Sounds fine for me for a first time in Italy, although Pompei (from, and back to Rome in a day) will kill you. Perhaps you could plan an extra day (not delete it from the other two cities) and stay overnight in Naples and get to see the Museum, several sites in town (e.g. Cristo velato and more), enjoy pizza, sea food and the views. Or, of course, you plan all of this in a second visit in a year or so.