Regarding SSO saml response

Is there any possible answers for the below?
we are going to publish an app in OKTA marketplace.

1.What is the way to get the domain name with saml response for SSO?
2.How can we get the list of users in an org domain -any api is there-if api is there means how we can authenticate with our app?
3.If we submit an app for OKTA verification how long it will take to see in search applications?
4.How can we identify this user is admin and this is not admin?