Unity IAP Subscription Doubts

At present I have completed implementation upto successful transaction of monthly subscription product. But now I want further explanation into this:

1. In which case can we use local receipt verification? because mostly its a risky thing to depend on local receipt.

2. Whether local receipt will automatically get updated when transaction happen for auto renewal subscription?

3. If I was depend on local receipt content then at which time I require to refresh its content?

4. How to update local receipt content?

5. If I was sending base64 key to my custom server, so custom server require to call on which url? Give me some document link if exist.

6. I require to send base64 key to my custom server -> custom sever will sent this key to apple server-> apple server provide reply in json format -> custom server reply back to me json format, Is this correct step I have mentioned for subscription verification process?

7. At which place in code I require to check for expiration of subscription? I have used following script in coding:Integrating Unity IAP In Your Game

8. I have purchase auto renewable subscription but in sandbox environment its not auto renewing, each time I require to purchase it for testing purpose. Is this normal process?

I want above doubts reply so I can move ahead in implementation.