1)Do we have to separately install IOSXR image in active and standby RP and how to check that current IOSXR image of active and standby RP(command) [SM] - No, if the standby tries to boot with no image or a different image it will sync to the active RSP for the correct image and configuration
2)Do we have to manually enable NSR/NSF for redundancy also is there any CPU impact if enable NSR/NSF? [SM] - yes you need to enable per protocol, NSR and NSF do have CPU and memory impact.
3)Is NSR/NSF mandatory configuration on dual RP router ? [SM] - Not mandatory but virtually nobody runs without them. If the active RSP goes down you dont want to waste 5+ minutes relearning the entire BGP table or blackholing traffic
4)If there is no NSR/NSF what is going to happen when active RP goes down ? [SM] - you lose all routes for that protocol as the neighborships will bounce.
[SM] - So dual RP will sync the two RPs (RSPs) to a point, the OS and configuration are synced. Other files are not synced. With NSR and NSF session state for your protocol is synced between the two RSPs so both RSPs have communication to the peer and the same routes etc. Any action you take on the active will get synced to the standby, such as software change, and config change.