I have also made a lot of changes to my 1972 house because I want to save money. I also have a drilled well and septic. I changed all my toilets and washing machine based on the amount of water going into my leach field.
I added insulation to attic, insulated hot water pipes, replaced exterior doors and caulked forever.
I even took off my exterior wall electric outlets and foamed around them. I live in NH where we are more concerned about heating than cooling.
How long will your invertor last? What will it cost to replace?
Nobody ever mentioned it to me as an issue that might need replacement. The system is approaching 4 years old and no issues so far.