Sept is Ireland is pretty moderate, not bad at all. It won't get very cold although it may get damp. SW Ireland is still one of my fav cycling spots and I have been back three times.
There are a couple of hills which take 20mins to climb but they are not particularly steep. There are plenty of short, sharp little hills but only 5 mins climbing.
The problems in France are restricted to a few big city suburbs, not exactly prime cycling country.
Italy in Sept can get cold and wet as well as warm and dry, esp in the Alpine regions.