Hi,
>1. Stop SQL server reporting server, Please confirm whether this step is mandatory while upgrading. Or, It's automatically migrated via setup /SqlSetup_x64_ENU. Correct
Quoting from the document-Upgrade and Migrate Reporting Services:
Upgrade to Reporting Services 2017 and later from Reporting Services 2016 and older isn’t the same upgrade scenario as in previous versions. When upgrading to Reporting Services 2016 and older versions, you could following an in-place upgrade process using SQL Server installation media. When upgrading to Reporting Services 2017 and later from Reporting Services 2016 and older, you can’t follow the same steps because the new Reporting Services installation is a standalone product. It's no longer part of the SQL Server installation media.
>2.Full-text Upgrade. Which option it keep all the original Full-text catalogs?
Import. An imported full-text catalog does not use the new word breakers installed with the latest version of SQL Server. To ensure consistency in query results, full-text catalogs have to be rebuilt.
https://learn.microsoft.com/en-us/sql/relational-databases/search/upgrade-full-text-search?view=sql-server-ver15#FT_Upgrade_Options
>3.Data Collection and Resource Governor become disable after upgraded.
These features are disabled by default.