If you have the skill to weld it, it will get you by until it starts to leak in another spot. Its really only a temp fix, since if it has coroded through at one point, it will at another. They commonly leak at the big gasket to the side tanks, you can tighten the crimps to get a few more miles out of it too.
And yes, just loosen the 32mm nut to remove the fan. But you can leave it in for rad replacement, just slip the shroud off and remove the radiator.