twitter limit is less than 1000, also you need to maintain the ratio of followers to following after the limit of 2000 people you follow
there are many app used by people to increase followers, but do take care of ban which twitter impose................. twitter is very strict
twitters moderators are wise to people who are following large numbers of people and get suspicious if you follow too many. However if you were a celebrity it would be normal to get a large following so they would not be so suspicious in this circumstance. it is all to do with why you are having large amounts of followers or are wanting to follow large amounts of people twitter will make an assesment based on your behaviour so be moderate with your followers unless you are famous