I dug out anf finished a 600 sq ft basement and found out in summer all
I needed was a return, But my AC cooled the basement to 65 from
uninsulated ducts, making it cold. So I insulated the ducts now it is
warmer in summer but colder in winter so I added supplys, for winter.
Do it right the first time I learned the hard way. I had excess capacity
from my hvac, that should be your first question.