1. Can't do anything about it as Spark is not doing any lookup for the name in this field. It just copies the text you have entered into search field and omits anything starting with @. Well, i'm assuming it doesn't look for the name, based on my testing.
2. You don't need plugins for this. Just create some groups on the server, add users to those groups, then go to groups' settings and enable contact list group sharing, put a name for a group and share it with All users or selected groups. This way Spark will display names of users, which where provided during user creation in the Admin Console. If you have LDAP integration and pull users from AD, then i'm not sure how users will show up.
3. There is no such plugin and i don't think anybody is working on it.