I doubt that COL is of much concern to OP’s nephew based on his current location in New Jersey and based on the new DH Horton community (over $1 million townhomes) being considered in Falls Church.
Personally, I prefer a more racially diverse community like Old South Alexandria. But I am not OP’s nephew. Demographics may or may not be important to him.
All of the communities under consideration are economically upscale & wealthy.