Two considerations when installing a managed package in a sandbox are:
The installation link has to be modified to test.salesforce.com, because the default installation link points to login.salesforce.com which is for production orgs. To install a package in a sandbox org, the administrator has to replace login with test in the installation URL before clicking it.
The package will be removed any time the sandbox is refreshed, because refreshing a sandbox replaces its current data and metadata with those from its source org. If the source org does not have the package installed, then the sandbox will lose it after refresh. Any metadata changes to the package do not have to be recreated in production, because they are preserved during upgrades unless overwritten by the package developer. Install for Admins Only is not the only install option available; there are also Install for All Users and Install for Specific Profiles options. Reference: https://help.salesforce.com/s/articleView?id=sf.distribution_installing_packages.htm&type=5 https://help.salesforce.com/s/articleView?id=sf.data_sandbox_implementation_tips.htm&type=5

Contract is a standard object that represents a contractual agreement between your company and a customer. Case is a standard object that represents a customer's question or problem that needs to be resolved by your support team. Account is a standard object that represents an individual or an organization involved in your business, such as customers, competitors, partners, etc. These three objects are commonly used for service use cases in Salesforce. Reference: https://help.salesforce.com/s/articleView?id=sf.contract_fields.htm&type=5 https://help.salesforce.com/s/articleView?id=sf.case_fields.htm&type=5 https://help.salesforce.com/s/articleView?id=sf.account_fields.htm&type=5

A cross object formula field is a type of formula field that references fields from related objects using relationships such as lookup or master-detail. It can be used to display data from one object on another object without creating another relationship or copying data. A cross object formula field can be created on opportunity object to display data from industry field on account object using account ID lookup relationship. A custom account field, a standard account field, or a master-detail relationship field are not types of fields that can display data from industry field on account object on opportunity page layout; they either do not exist or do not reference related objects. Reference: https://help.salesforce.com/s/articleView?id=sf.cross_object_formulas.htm&type=5

To automate applying discounts on opportunity products when an opportunity is won, the administrator should use Flow Builder, which is a tool that allows creating complex business processes with clicks. The administrator can create an autolaunched flow that runs when an opportunity is updated, checks if its stage is "Closed Won", and updates its related opportunity products with discounts from a formula or variable. Approval Process, Prebuilt Macro, and Formula Field are not able to update related records based on criteria. Reference: https://help.salesforce.com/s/articleView?id=sf.flow_build_overview.htm&type=5

The Assignment Rule checkbox is a checkbox that appears on manual case creation pages when assignment rules are defined for cases. The Assignment Rule checkbox determines whether or not to apply assignment rules to manually created cases. If the Assignment Rule checkbox is selected by default, then any manually created cases will be assigned according to assignment rules instead of being owned by the agent creating them. To prevent this from happening, an administrator can either deselect the Assignment Rule checkbox when creating cases manually; or change the default setting for this checkbox under setup by selecting or deselecting Use active assignment rules by default. Reference: https://help.salesforce.com/s/articleView?id=sf.customize_casesupport_assign.htm&type=5