How many planets typically surround one star?
No one knows.
To date, only a few thousand possible planets have been discovered outside our solar system. At present we do not have the technology to look at those planets like we would a planet in our solar system.
Statistically, it is nearly a sure thing that life exists on many other planets in probably every galaxy (300 billion) in the universe. Within that likelihood exists the probability that intelligent life exists elsewhere in the universe.