Re: shorten activity excerpts
you could shorten them via a filter prior to updating the db. it just depends on the component as each have their own filter on the content.
'content' => apply_filters( 'bp_activity_new_update_content', $activity_content ),
or the filter on the activity templatetag
apply_filters( 'bp_get_activity_content_body', $activities_template->activity->content, &$activities_template->activity );