It feels like a good idea to be ready for a command line upgrade, even if about to attempt a web one. Personally I check this forum beforehand, to see if anyone has any difficulties at present. It can happen that the codebase is temporarily broken. Also, I always take a backup and download it before starting.
I gather the best practice if minimal downtime is important is the two container installation.
I don’t fully understand Docker (an understatement) but I gather that if you find yourself with a half-upgraded forum which isn’t working you can in some sense start up the pre-upgrade version while you wait for help. (I searched for “restart the old container” but didn’t find the exact information for this.)