1 - It is not in our recent objectives to integrate solr as the default search system in our Moodle stack. Any case it seems very interesting and we are going to study it. We will keep inform of that.
2 - We have no official documentation for such task. But it is possible. Anyway, (here)[https://docs.moodle.org/31/en/Global_search] and (here)[https://moodle.org/plugins/tool_coursesearch] you can find quite good and new guides to achieve what you are looking for.
If you have any other question and you think we can help, please don’t hesitate to ask.