The general metrics I've observed on Instagram to show success:

- have at least twice as many followers as you follow

- have at least 10% the number of followers as likes per pic

So, you could have 700 followers, but follow no more than 350 people, and must get 70 likes or more per pic. That's "success." Granted, as you get into 2,000+ followers, it can get harder to maintain the 10%.