The deployed permission set will merge with the existing permission set in production, meaning changes made in the sandbox will be added to the existing permission set after deployment.
Reference:
Salesforce Help - Permission Sets

Schema Builder is a tool that presents a comprehensive view of all relationships in one place. It allows app builders to see how objects are connected and create new relationships. Lightning Object Creator, Object Manager, and Lightning Record Page are not tools for viewing relationships, but for creating objects, managing fields, and customizing record pages respectively.

The app builder should use Sum as the type of summary in the roll-up summary field. A Sum type of summary allows the app builder to calculate the total value of a numeric field from the child records related to a parent record by a master-detail relationship. The app builder can create a roll-up summary field on the Account object that sums the Amount field from the won Opportunities related to each Account. Count is not a valid type of summary, as it does not calculate the total value of a numeric field. A Count type of summary allows the app builder to count the number of child records related to a parent record by a master-detail relationship. Max is not a valid type of summary, as it does not calculate the total value of a numeric field. A Max type of summary allows the app builder to display the largest value of a numeric or date field from the child records related to a parent record by a master-detail relationship. Min is not a valid type of summary, as it does not calculate the total value of a numeric field. A Min type of summary allows the app builder to display the smallest value of a numeric or date field from the child records related to a parent record by a master-detail relationship.