Five-0 is a name created by Steve so there is no way Graham would know what that means as the public hasn't heard the name enough.
One of the medications that Danny finds in Wilson's home and tells McGarrett is clonazepam. McGarett says that it's an antipsychotic and can sometimes be used for PTSD. It can be used for PTSD but also to treat many other things as clonazepam is a type of benzodiazepine, not antipsychotic. Benzodiazepines are a class of medications that treat anxiety disorders, as well as being used as sedatives for insomnia and panic attacks.
At the beginning of the episode when Graham is fleeing the cops, you see HPD officers. Since Ford Island is a military installation, it should have been Navy Police.