Why it should probably be the President initially is a much longer answer, but as far as only targeting specific businesses the answer boils down to not every Chinese businesses being viewed as a problem. If you only view certain companies or industries as strategically significant at the moment then why would you want to ban the rest? That just drives prices for imported goods higher while accomplishing nothing of value.

Ok no problem. If you want to live in a country where the emperor decides on this, it's not my problem.

The emperor isn't deciding this. The president is using authority which is granted to him by law. In this case a law which includes a means for Congress to overrule his decision if it wishes.

India implemented the ban first. Donald is simply copying what India did.

I agree with you. Should be a blanket rule