Originally Posted by RAI

What is Ally limit (The maximum number of allies you can have) tied to? There's no option in the store to buy more I think. Is it just level, and if so what are the thresholds for getting more (is there a cap?)

I checked the FAQ and did a few searches, but not finding anything related.

There are some quests that unlocks allies slots. I think it's for completing the story missions.