Has anyone kept guppies, mollies, barb, .... in a pond ?

I have kept all of the above in a pond, but it was an indoor tropical pond. I doubt your guppies, mollies, tetras, or gouramis would survive with those drastic temperature shifts. I would normally say that a lionhead goldfish would probably be fine, but 90 degrees is pretty toasty for them. One year when my outdoor pond got outrageously hot from a heat spell, I lost several of my koi. Barbs are definitely fish that can tolerate colder temperatures, but I'm not sure if as low as 40 is okay.