Go buy an off-the-shelf kitchen vent fan as big as they make. You will probably run this fan 24/7. That will determine the cfm you will need for the air supply (air into the room). Based on the cfm we can tell you the diameter of the duct you will need to run from the south wall to supply the air to the room. Bigger ducting is always better and necessary if there are too many 90 degree elbows. If you need to make a 90 degree turn, use 2@45 degrees... less friction.