Limitations of secure storage – KeyChain and KeyStore

I’m planning to use flutter_secure_storage in my app to keep some private keys and tokens.
I’m looking for limitations of secure storage on both Android and iOS but I cannot find answers to some of the questions:

  1. How big is KeyChain and KeyStore storage on iOS and Android, respectively?
  2. How many keys can we store inside?
  3. How big can individual key be?
  4. What is lifetime of the storage? Does it exist only while app is installed? Is it persistent of ephemeral?

Thanks

Source: Ios Questions