Installed steel front door. I am going to paint it black. I just primed it with gray primer.

1. Should I put 2 coats of primer?

2. How long should I wait before I start painting it black? Few hours, tomorrow?

Installed steel front door. I am going to paint it black. I just primed it with gray primer.

1. Should I put 2 coats of primer?

2. How long should I wait before I start painting it black? Few hours, tomorrow?

From past experience, i would say yes 2 coats of primer.
Let it dry good, paint tomorrow. Also watch out if you have a glass storm door, if so leave it open, sun beats down on it and temperature gets really hot between storm door and front door. Either leave the storm door open or keep it closed and leave front door open until paint dries. Have seen it cause bubbles in the paint. Learned this the hard way.

Installed steel front door. I am going to paint it black. I just primed it with gray primer.

1. Should I put 2 coats of primer?

2. How long should I wait before I start painting it black? Few hours, tomorrow?

Primer doesn't need two coats if you do it properly. A good oil-based primer is the best, but you have let it dry well before painting. I'd also recommend a water-based latex for painting. If you use oil-based paint, and water gets under it eventually, it will start to crack.