Selecting one habitable planet as place for story is somewhat easier - just thinking of one planet that does not violate laws of physics. But I need more and want to have realistic proportions. Assumptions - panspermia and carbon chauvinism; by habitable I mean: has life that's able to produce oxygen and at least in lucky conditions unprotected human would be able to breath for a while. 1)Which stars? Red dwarfs? Orange dwarfs? Yellow dwarfs? Multiple systems? I know that red dwarfs are the most popular ones. Should that mean that I shall realistically assume that the majority of habitable planets is around them? (yes, presumably after eliminating flare stars) Same question concerning systems with more stars - should their popularity mean more planets, or neglect them because of unstable orbits? 2) Popular size of planets/exomoons? (Should smaller than Earth actually be more popular) 3) Temperature? Actually estimates concerning Goldilocks zone starts just before Earth and ends even after Mars. Does it mean I should assume actually a majority of planets colder than Earth? 4) Relation of exomoons to planets? (Should I treat hot jupiters as rare anomaly that's merely easier to observe, and big enough moons around them as even rarer anomaly?) 5) Odd axial tilt or seriously eccentric orbit? (should that be popular?) 6) Should I assume that in general big planets tend to be water worlds (keeping volatiles is easier), while light planets/moons are more desert ones with thin atmosphere? Any other suggestion?