As xox said I would 100% insulate the walls with something that has r-vlaue. I'm in a michigan basement, insulated my walls with R13 rolls and did foam board over the top. Super stable temps and easy to monitor. Not sure of your geographic location but I think a mini-split might be overkill. I have a 12X15, run led's, CO2, 3 Hurricane fans, dehumidifier and pump in cool air from the basement. Room temp is 78 during the day and humidity is 45% at all times....don't overthink it and invest a ton of money on the first round. Find out what works for you and upgrade later if needed.