"While only about a dozen planets have been confirmed in the habitable zone, the Kepler spacecraft has identified a further 54 candidates and current estimates indicate "at least 500 million" such planets in the Milky Way.[6]"
http://en.wikipedia.org/wiki/Habitable_zone
As to battered with asteroids yes they will have been or still are, but so was earth
Being in a proposed habitable zone does not make them habitable......


