IS
No, use "is" instead.
The way you said that is grammatically correct if that's what you were asking.
No, it is not.
Yes, it's correct to say politics is as in, "Politics is the business of politicians." It is also correct to say, "Many kinds of politics are played in Washington."
It can be correct to say you are always welcomes. It is correct when finished with "in my home or at my place of business."
Yes this is acceptable grammar.
Business premises is correct, just as you have it.
if you are talking about your boss specifically or if you are working with a sole employer you say employed by. If you are talking about a business as a whole you say employed at.
The correct spelling is "business"
The correct spelling is business.
The correct spelling is business.
The correct spelling is "business".