The leak in the radiator overflow is not as important as your overheating. You can repair that with silicone or some other sealant or replace it. But, first you need to find out why your fans are not coming on as that is what is causing the overheating. The first things to look at are the relays and the temperture sensor. There are genrally 2 temp sensors and they are near the thermostat in most cases. If your car has a temp gauge there will be 2 off them. One with one wire and one with a few wired. You wnat to replace the one with several wires as this is part of what turns your fans on. You also wnat to make sure the fuses are oaky. There also may be a fan switvh near the radiator. The relays will be in the elctrical harness near the fans and the will be the last component before the power reaches the fans. You may have to do some tracing to find them.
Replace the sensor and the relays. You might want to get a Haynes manual from a local parts store as they will help to identify the proper location and part to replace. They are very helpful as they have actual pictures of the locations.
Let me know if that gets the fans to come on and gets the car to stop overheating.