I found one important message to all twitter users that is you can’t follow more than 2000 people in twitter if you don’t have enough followers. once you reach your limit then you can’t follow anymore. One popup will warn you!!
Alert Message when you try to follow 2001th people
Here you can see the official follow limits message from twitter support
Technical Follow Limits
We do not limit the number of people who can follow you, but we have put limits on how many other accounts you can follow.
Every account can follow 2,000 users total. Once you’ve followed 2,000 users, there are limits to the number of additional users you can follow. This number is different for each account and is based on your ratio of followers to following; this ratio is not published. Follow limits cannot be lifted by Twitter and everyone is subject to follow limits, even high profile and API accounts.
In addition to this account-based limit, every Twitter account is technically unable to follow more than 1,000 users per day. Please note that this is just a technical limit to prevent egregious abuse from spam accounts. Accounts are also prohibited from aggressively following other users. OurFollow Limits and Best Practices Page has more information on Twitter’s following rules.
complete rules of twitter twitter.com/rules
Help center https://support.twitter.com/forms/general
Happy tweeting with freedom 