As to your first question regarding updating a set of records of entity A when inserting a new record of entity B: you could set an event handler on the entity B that performs the business logic that updates records A (e.g. after create of B). Or you could add this business logic in a custom save microflow when saving B (if B is entered by a user). Read more about event handlers here: https://docs.mendix.com/refguide/event-handlers

As to your second question: jobs can be scheduled using scheduled events as described here: https://docs.mendix.com/refguide/scheduled-events