Three completely different scenarios I would say.
Ghosts I'm sceptical about - If they existed I would expect to see more evidence. If they do "exist" my theory would be more of an echo, or trace of a former existence or event rather than a sentient being.
UFO's seem quite feasible. Look up at the sky, count the number of stars and then ask yourself do you really believe this is the only place in the universe where intelligent life could have evolved. A mere 1,000 years the concept of flight, radio, television, the car, electricity, and so on would have been witchcraft, who can say what a civilisation just 1,000 years more advanced than us could achieve.
Regarding god, I am extremely doubtful for many reasons but I would say anyone who categorically denied the possibility is at least as deluded as someone who is adamant that their theory of god and religion is correct.
Have I affronted everybody? Good.