Compounds that have the same molecular formula but different chemical structures are called isomers. Depending on what types of differences there are between the structures, it is possible to classify isomers into various sub-types.
The Limit. You can follow up to 7,500 users before receiving the aforementioned error. Instagram invoked this limit to reduce spam in their system and keep users in compliance of their Community Guidelines. However, some users can follow more than 7,500 users if they did so before Instagram imposed the limit. Some Instagram users also claim there's an hourly or daily limit to the number of new followers you can acquire, but Instagram has not confirmed such restrictions.
The answer: yes and no. With standard Instagram posts, there's no way to track who's looking at your posts or visiting your profile. One sort-of exception: You can see the amount of views on a video or Boomerang post, but Instagram won't reveal who exactly interacted with them, only how many people did. Fortunately, there's another way to discover your most loyal and curious followers.