In most cases it's best to reach out and connect with experts in the industry.  This may seem expensive, time-intensive, etc., however this usually resolves issues and leads to improvements much faster than try-and-fail or oversimplifying what experts have learned through years of training and experience.

What is the most efficient data center?

I am working on a ranking list.  It should be noted that there are a lot of different types of DCs and different metrics (beyond PUE) are needed for comparison.

How much energy does a typical data center use?

Depending on the type, a data center typically uses many megawatts (MW) of power, with some well over 100 MW.  A typical home uses about 10 MW hours per year; a data center that uses 1 MW uses 8,760 MW hours per year.

How big are data centers?

Once again, depending on who they support, they can range from an over-sized closet to large campuses with many buildings of 200,000 square feet each.