probably the best cycling weather you can ask for in the Alps: still warm but not hot, and more importantly, without the so frequent afternoon/evening rainshowers of summertime. However be aware that it can get quite chilly quite fast up there. Never ride without rain gear and warm clothes

that depends on your athletic ability and your fitness level; however, travelling so light, it shouldn't be a major problem


maybe you can find this chart useful in planning your route (it's a list of almost all relevant climbs in France)