Making a maximum of 150 people participate is fine.
I think it would be quite good to only count those with 10 (or more) games in the rating. This will reduce the amount of work and make the tables less cumbersome.
I've written many times about removing entries. Let's have you think about why this is impossible; there are several reasons. A hint to one of the reasons: two players participate in the game; by removing one, we invalidate the result for both, so....
But in the middle of the table, there are many people with 1 or 2 matches – they played and disappeared; these should not be counted; for example, consider them in the ranking only after 5-10 games.
the dependence should not be on the number of games, but on time. There are a lot of players who haven't played Heroes for 3-5 years.