As for your last question, can you please debug the code within the function. Can you confirm that the filter is fireing?
Perhaps there is a problem with the filter using the ‘name’. Instead, can you try using the field key?
There is no need to write a new field type.
As for AJAX JS stuff, this would take quite some time for me to explain, so I encourage you first to jump on google and research how to add JS to an admin screen (there is a ACF action called acf/input/admin_head) for this, and also learn how to perform an AJAX call.
Welcome to the Advanced Custom Fields community forum.
Browse through ideas, snippets of code, questions and answers between fellow ACF users
Helping others is a great way to earn karma, gain badges and help ACF development!