Yes, there are ways to do this in open source. It is a little more labor intensive, obviously.
1 - Check out this article:
2 - Interacting with databases, as long as they are available, is pretty straightforward. You can either connect and commit transactions and queries as needed, or connect the database to the flask server.
3 - Yes, you can perform SSO services and Active Directory with Flask_Login and use the current_user to filter your data:
4 - That can either be handled by crontab on a linux server, or some other task task manager to submit the request. If you are going to store this as a cache, you could look into CosmosDB from Azure.