what's the proposed way to close individual questionnaires/waves? Should we use the Internal/locked access restriction?
Yes, you can use the access restrictions. Or you may use a PHP code snippet on the first page:
if (time() >= strtotime('2020-06-11')) {
text('finished');
buttonHide();
pageStop();
}
When should we use the 'Survey finished' button under 'Project Overview'?
There is no need to use that button at all. It will only display you different information. If the survey administration period has finished, the project will automatically enter that project phase.