What size heat pump should you have installed in a new home in central Virginia with 2700 square feet?

Depends on cubic feet too, not just square feet. High ceilings such as cathedrals and trays make a difference, as well as the number of Windows. Another consideration is one story or two story. I always prefer separate zones for each story.

That said, I would estimate 5 to 6 tons for 2700 square feet single story with normal window situation and standard ceilings. Minimum 13 SEER.