Your estimate of amount of worlds in this galaxy isn’t right. You wrote there are possibly 8 habitable worlds in 150.000 stars. You also wrote there are opproximately 200–400 billion stars in our Milkyway Galaxy. That accounts for a share of 0,00005333333 % of 150.000 stars. So multiplying that by 200 billion stars is 11 million habitable worlds in our Milkyway Galaxy alone, not 40–80 billion :\