To protect data with backups by using Data Export Service, two considerations that the administrator should remember when scheduling export are:
* Data Backups are limited to weekly or monthly intervals depending on edition and license type
* Metadata backups must be run via a separate process such as Metadata API or change sets because Data Export Service only exports data (records) Metadata backups are not limited by sandbox refresh intervals. Data Export Service should be run from production orgs unless testing purposes require otherwise. References: https://help.salesforce.com/s/articleView?id=sf.data_export.htm&type=5

A roll-up summary field is a type of field that calculates values from related records, such as the count of child records or the sum of a field on child records. In this case, the administrator can add a roll-up summary field to the open house object to track the number of visitors by counting the child records on the visitors object.
References:
https://help.salesforce.com/s/articleView?id=sf.fields_about_roll_up_summary_fields.htm&type=5

Standard objects are objects that are included with Salesforce by default, such as Account, Contact, Lead, Opportunity, etc. They have predefined fields and functionality that support common business processes.
Custom objects are objects that you create to store information that is specific to your organization or industry.
You can create new standard objects using the Object Manager in Setup. References:
https://trailhead.salesforce.com/en/content/learn/modules/data_modeling/standard_and_custom_objects

Manual sharing allows record owners to share individual records with other users or groups. This is useful when one-off sharing is needed for a specific situation. Hierarchical sharing, criteria-based sharing and owner-based sharing are not suitable for this scenario because they are based on predefined rules or roles that do not match the requirement. References:
https://help.salesforce.com/s/articleView?id=sf.sharing_overview.htm&type=5

Picklist values, help text, and decimal places are three aspects of standard fields that an administrator can customize to suit their business needs. Picklist values are the options that users can choose from a picklist field; they can be added, edited, or deleted by administrators. Help text is the text that appears when users hover over a field; it can be customized by administrators to provide additional information or guidance for users. Decimal places are the number of digits that appear after the decimal point in a number or currency field; they can be changed by administrators to adjust the precision of the field values. Field history tracking and field name are not aspects of standard fields that can be customized; they are only available for custom fields. References: https://help.salesforce.com/s/articleView?id=sf.customize_picklists.htm&type=5
https://help.salesforce.com/s/articleView?id=sf.customize_fields_edit.htm&type=5
https://help.salesforce.com/s/articleView?id=sf.customize_fields_number.htm&type=5