How can an architect find information about who is creating, changing, or deleting certain fields within the past two months?

DreamHouse Realty has a data model as shown in the image. The Project object has a private sharing model, and it has Roll-Up summary fields to calculate the number of resources assigned to the project, total hours for the project, and the number of work items associated to the project.
There will be a large amount of time entry records to be loaded regularly from an external system into Salesforce.

What should the Architect consider in this situation?

DreamHouse Realty has 15 million records in the Order_c custom object. When running a bulk query, the query times out.
What should be considered to address this issue?

Universal Containers (UC) is in the process of migrating lagacy inventory data from an enterprise resources planning (ERP) system into Sales Cloud with the following requirements:
Legacy inventory data will be stored in a custom child objects called Inventory_c.
Inventory data should be related to the standard Account object.
The Inventory_c object should Inhent the same sharing rules as the Account object.
Anytime an Account record is deleted in Salesforce, the related Inventory_c record(s) should be deleted as well.
What type of relationship field should a data architect recommend in this scenario?

Which two best practices should be followed when using SOSL for searching?