When you transfer billing ownership of your subscription to an account in another Azure AD tenant, you can move the subscription to the new account's tenant. If you do so, all users, groups, or service principals who had role based access (RBAC) to manage subscriptions and its resources lose their access. Only the user in the new account who accepts your transfer request will have access to manage the resources.
Reference:
https://docs.microsoft.com/en-us/azure/billing/billing-subscription-transfer
https://docs.microsoft.com/en-us/azure/billing/billing-subscription-transfer#transferring-subscription-to-anaccount-in-another-azure-ad-tenant

You need to assign the user the Key Vault Secrets Officer role.
In the Azure portal, type Key Vaults in the search box, select Key Vaults from the search results then select KeyVault11641655. Alternatively, browse to Key Vaults in the left navigation pane.
In the key vault properties, select Access control (IAM).
In the Add a role assignment section, click the Add button.
In the Role box, select the Key Vault Secrets Officer role from the drop-down list.
In the Select box, start typing User2-11641655 and select User2-11641655 from the search results.
Click the Save button to save the changes.

To 'Read a storage account', ie. list the blobs in the storage account, you need an 'Action' permission.
To read the data in a storage account, ie. open a blob, you need a 'DataAction' permission.
Reference:
https://docs.microsoft.com/en-us/azure/role-based-access-control/role-definitions

https://docs.microsoft.com/en-us/azure/role-based-access-control/custom-roles