Hello anon! ^^
The requirement is different for every store, but usually they require 5,000 followers. Some storenvy ones don’t have a requirement for affiliates (they might for sponsorships) such as syndromestore, hhotaru. For storenvy I still recommend you start after you have at least 1,000 followers, since they usually give you a code and if it’s used a certain amount of times they will sponsor you.
I do recommend all the shops that’s in my shops bar, they’re all quite trustworthy and pays on time ^^