Data Loader supports bulk import/export.

Creating multiple similar products and distributing the skew across those products can be a way to mitigate issues related to lookup skew. The article explains that lookup skew happens when a very large number of records are associated with a single record in the lookup object, and this can cause record locking and performance issues. The article suggests creating multiple copies of the same product record and assigning different child records to each copy, so that the number of child records per parent record is reduced.

According to the Salesforce documentation, a relationship field is a field that allows linking one object to another object in Salesforce. There are different types of relationship fields that have different characteristics and behaviors, such as master-detail, lookup, indirect lookup, external lookup, etc.
To recommend a type of relationship field for this scenario, where legacy inventory data will be stored in a custom child object called Inventory__c, inventory data should be related to the standard Account object, the Inventory__c object should inherit the same sharing rules as the Account object, and anytime an Account record is deleted in Salesforce, the related Inventory__c record(s) should be deleted as well, a data architect should recommend:
Master-detail relationship field on Inventory__c, related to Account (option B). This means creating a field on the Inventory__c object that references the Account object as its parent. A master-detail relationship field establishes a parent-child relationship between two objects, where the parent object controls certain behaviors of the child object. For example, a master-detail relationship field can:
Inherit the sharing and security settings from the parent object to the child object. This means that the users who can access and edit the parent record can also access and edit the related child records.
Cascade delete from the parent object to the child object. This means that when a parent record is deleted, all the related child records are also deleted.
Roll up summary fields from the child object to the parent object. This means that the parent object can display aggregated information from the child records, such as count, sum, min, max, or average.

The Individual object is a standard object that lets you store details about data privacy and protection preferences for person accounts, contacts, users, and leads. The Individual object can be used to implement a standard communication preference management model for NTO, with relationships to the other objects.

To improve the dashboard performance, the data architect should use selective queries to reduce the amount of data being returned, de-normalize the data by reducing the number of joins, and reduce the amount of data queried by archiving unused opportunity records. These options will help optimize the query performance, reduce the query complexity, and free up storage space.