Margin requirement at IB

Hi, I have this question for IB but I have not heard back from them.

I come from the Forex side. Just like there is a margin requirement like 1:50 or 1:200 in Forex, is there a margin requirement for trading Stocks also?

I have a regular stock trading account at IB. Since so many members use IB here, can I ask, does IB have a margin requirement, how much, and under which does it issue a Margin Call?

Lastly, if trader is not getting a margin call, follower should not either, because Autoscaling should have reduced the lot size in proportion.

Is this correct?

Thank you.