We are located in Huntington Station, NY on Long Island, so we're in a similar weather zone as you being in Maryland.
For what it's worth we have a west facing sun room built in 1989 or so. The walls are 6", insulated and the entire west wall is 4 large insulated glass casement units and a 5' sliding glass door. The room is basically 24' x 16' with a cathedral/sloped ceiling coming from the existing house.
I guess it's called a 'shed', but whatever.........When we bought the house in 1995 it had a wood burning stove and an LP gas heater. I ditched the LP, but kept the wood stove, for better or worse.....
I decided a couple of years ago to put in a Mitsubishi mini split, and it was the best thing I ever did. I did the entire install in terms of the compressor outside, the indoor wall unit and running the electrical feed to the box.
I had an electrician do the actual box connection, and an HVAC guy we've used for many years came and did the hookup of the wall unit to compressor (or whatever the outdoor unit is called). I've given the guy so much work over the years he refused to charge me anything, but I tried......
Anyway.......it's so nice to be able to set it and forget it. I find that even in the winter I'll have to turn it off with all the solar gain in the afternoon. I have many very nice guitars, so there are times where I'll use the dehumidification setting, but more often than not I have a humidifier going to keep the room around 45-55%.
Our sinuses like that, too!
Here's some pictures to give you an idea of the installation:
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The outdoor unit is directly below the wall unit, and it's mounted into the concrete foundation with wall brackets, and I attached a honey combed plastic shed roof above it for snow protection.
We rarely use the wood stove anymore, but it's there in a pinch or power outage.
Best of luck with the install!