Case 1) Loading one field on the PHP side base on another field makes little sense without using AJAX, simply because new fields have no value and this means that the post must be saved every time F1 is change in order to change F5. In order for ACF to update F5 it would have to make that AJAX request.
Case 2) The problem with case 1 multiplies the issue for case 2. Being generated in PHP and knowing how ACF works, it simply isn’t possible to show different choices in different instances of the same field, at least not in PHP. Using JavaScript, this is possible.
ACF can do some complex things but I don’t think what you’re looking for will ever be possible without doing quite a bit of custom JavaScript and AJAX coding. Then again I’m not the developer.
