For 4k and so not to have to fuck about swapping for bigger unit, go straight for a 21k BTU aircon, they are gonna generate alot of heat. Cool tubes will be a must in the summer months. You wil need taht heat in the winter months so get yourself a fan controller to adjust extraction rates throughout the year.
^^^ What he said but if you want and imo you should get a couple or a few low power fans and set up duct work and use the fans to help blow the cold air around the area a little better.