You'll probably need to call a company like Amerigas about the propane, both the tank and the gas may be theirs and can only be collected by them. After that, just call an HVAC guy or company to have the fireplace removed along with any piping or wiring.
- The HVAC technicians can give you the best recommendations on the Mini-Split manufacturers, as they only fix the bad ones on a regular basis. Good ones are maintenance free for at least 10-years...beyond hosing off the outdoor condenser box's internal fins whenever debris is noticed.
- Once that's all figured out and whatever replacement is installed, you'll need a Skilled Handyman, Mason or Carpenter to get the building and room back to the fireplace never having existed. Selling the fireplace is probably not an option (outside of a Metal Recycling Center that you take it to), as safety regulations have likely changed since its manufacture...just have the HVAC guy or company haul it away.