Re "My first question: I edited a template: https://gom.wikipedia.org/wiki/Template:Welcome , but it doesn't get updated in Flow page descriptions where it's transcluded, for example: https://gom.wikipedia.org/wiki/User_talk:The_Discoverer":
Unfortunately, this is a known issue (phab:T125857). The only workaround is to edit the content, e.g. the description.