Just want to make sure, if I set the appliactions to public, and set the rank to Officer .. only officers will see it? We just promoted new officers and they cant see any of the previous applications. Just want to try and avoid that in the future if we promote other officers.

If the applications are set to "Private Thread", it doesn't change the access list of previously submitted applications. This is by design to effectively prevent someone from ever seeing their own application (when in private mode).

If you wish newly promoted members to see old applications, you need to set the threads to non-private mode, and make sure that the target thread tag's rank is set properly.