Random questions about playing Terran

I am a platinum level terran player who is trying to get into diamond and have a few questions in order to improve my play.

1. When you make a second command center, how many workers should you transfer?

2. When do you stop making scvs?

3. Does anyone have suggestions for sim city to defend against drops and zergling counter attacks?

4. When are some good general timings to attack against the different races?

The only reason I got into platinum is because of my decent macro but I need to improve in other ways as well so any other tips are appreciated. Thank you.