C: The Web Form Step record contains a field named Custom JavaScript that can be used to store JavaScript code to allow you to extend or modify the form's visual display or function.
D: You can add custom Javascripts to Entity lists.
Reference:
https://docs.microsoft.com/en-us/powerapps/maker/portals/configure/add-custom-javascript
https://docs.microsoft.com/en-us/powerapps/maker/portals/configure/entity-lists#add-custom-javascript

A: When you import a managed solution, all component changes will be brought into the environment in a published state.
B: You can apply patches to either managed or unmanaged solutions and include only changes to entities and related entity assets. Patches do not contain any non-customized system components or relationships that it dependents upon because these components already exist in the deployed-to organization. At some point in your development cycle, you can roll up all the patches into a new solution version to replace the original solution that the patches were created from.
Reference:
https://docs.microsoft.com/en-us/powerapps/maker/common-data-service/import-update-export-solutions
https://docs.microsoft.com/en-us/power-platform/alm/create-patches-simplify-solution-updates

1 - Register the application in Azure AD with appropriate permissions.
2 - Use the Dataverse application user username and password...
3 - Create the application user in Dataverse using the Application User form.
4 - Assign a security role to the application user in Dataverse.