Had a similar plan to add one of those units to my basement when we bought our house in 2016. It’s a walkout finished basement containing my woodworking shop, theatre room and an area for the train layout. It has no a/c and the only heat is a wood burning stove.
Decided to wait a year for my bank account to recover after buying the house. In the meantime, started to track how many days I would need a/c and heat with a digital thermometer that records history. Figured that info would help in buying an appropriate size unit.
Now going on three years and have had no days that I needed a/c. The heat is only justifiable during an average of 14 weeks. So far, on occasional fire in the wood burning stove or an electric space heater is all that is needed to make it comfortable. The highest recorded temp was 74 and the lowest was 59. Current temp is 68. Hard to justify the expense for a nice split unit so far. Besides, the wife likes the excuse to have an occasional fire while watching a movie on the projector.
We did buy a dehumidifier that I run occasionally during the humid Virginia summers. Highest recorded humidity so far has been 64 percent. Prior owners did a nice job of sealing the basement and adding a good layer of spray foam insulation in the walls.
