The requirements for getting on Solo, FFA and Teams leaderboards are:
at least 2 games played within the last two weeks
at least 20 games total
of the leaderboard's rating type.
Champions formula: there're 2 types of champion: standard champs and variants champs. For #1-20 on a leaderboard, you get 100,80,60,50,40,35,30,25,20,15,12,10,8,7,6,5,4,3,2,1 champ points respectively.
Games Played: both rated and casual games count. Aborted games do not count.