Question

Are stars with planetary systems very common or extremely rare?

Answer 1

Exoplanets are quite common.

Explanation:

Wikipedia (https://en.wikipedia.org/wiki/Exoplanet) reports that that there is at least one planet per star on average, and more than 1000 exoplanets were verified in May 2016 alone. There may even have been exoplanet sightings outside the Milky Way Galaxy!