A. Yes, the rule of thumb is you need 25 times of the amount you need to spend in your retirement time.
For example, you figured out you will need $100,000 per year to live a comfortable retirement life. Your annual social security income is $60,000. So you will need 25*$40,000 = $1,000,000 to retire. In other words, you can withdraw 4% per year from it to support your retirement life without incurring the risk of running out of money when you are still alive.