Hello @Mahesh_Gunaje
1. If this is a Persistent query which works on GET method, I don't think we have option to enable authentication apart from CORS setup on Dispatcher server.
2. It's not allowed with AEM Graphql to update the CFs. Best practice and Adobe recommendation is to use Rest APIs (Assets Api) to update the CFs.
3. Yeah, it should be fine. We can expose the Asset path which 3rd party or Mobile app can consume and use it on UI.
Hope this helps