I would like to…
– MOVE “This entry was posted in (CATEGORY) on (DATE).” to the top, under the entry title
– leave the TAGS + EDIT link where they are (below the entry/comment link) on -individual- entries’ pages
– remove the TAGS on the -mainpage- entries
– add author to the end of the category/date line
But you should never modify theme files, especially a default WP theme – as you could create big problems and you will lose all your changes when WP is updated. Rather, create a child theme and make any changes there.