Little confused by your questions. My thoughts are "Why wouldn't you insulate, heat and have AC if it's going to be finished?" Assuming you have AC in the rest of the house. Usually easier to do that while finishing the rest of the space. Is the space going to be bedroom type area, rec room, any cooking or kitchen area such as an apartment?
Keep in mind that most ductless systems struggle on really cold days. I would recommend a secondary heat source. Great units for cooling. Very efficient and quiet