Hello @prakash_m,
I’m not sure if this is what are you trying to ask in 1 and 2. But this is what I have:
DiscoveryCallbacks are only adding new devices and updating existing devices and if a device is deleted in your cloud the expectation is that a command response, including stateRefreshResponse have a deviceError for that device specifying that it has been deleted.
Regarding point 3. Yes, a discoveryCallback will trigger a stateRefresh as the discovery reports new devices that are being added for which we need to get states for.
Hope this may help you.