Zoning -- Commercial with variance for residential

[Brandon Payne]

I am looking at a property that is zoned as commercial with variance for residential. The house was built in 1950. This would be my first purchase and I'm not sure how to go about judging this.

Where can I go to find specific information about zoning?
What does it mean for the lot to have variance for residential?

How do I go about assuring that it will be an appropriate zone for a buy and hold?

Is there a risk that it would arbitrarily change to commercial and the building be forced to be changed or demolished?