It might change in the higher lvls, but I think 1 star is about 1 cup/league lvl. That still gives a pretty big bandwith of opponents in the competitions, from 2-6 stars in the league, or up to 3 managerlvls in the cup. In my experience though, if you keep the draw/seedings as neutral as possible by unfriending everyone at your lvl, you'll likely end up pretty even leagues, plus/minus 1 star. As a result there's a big difference in league quality at every lvl, pairing the teams again by quality.