Replacing the furnace will allow you to market the property with an awesome, new fuel efficient furnace instead of a fuel hog that could break on any day.

Most older homes in SC are ventilated and breathe fairly well, so mold in the living space/attic typically isnt an issue unless there is a water leak where there is constant, excessive moisture.

Now that I own rentals my debt cycles with winter fuel and sometimes remodels being put on a credit card.

California charges a minimum tax of $800 a year per LLC, and more if you have gross receipts in excess of $250k.

If you make $150,000 as a W-2 and you have one rental that grosses $30,000, it'll just add fuel to the IRS fire.

I will honor my agreement of refinancing or doing a loan assumption as soon as I'm able (I've been trying excessively over the past decade), however if he does force a sale, can I tack on the fact that I've paid all expenses including the mortgage for the past now 13 years to demand he reimburse me half, or is he entitled to half the equity and I'm just screwed out of everything I've put into the house?

You may need to play around with how you word your request, so you won't get charged for an excessive amount of pages. 

There are lots of ways you could do this, but the execution is largely up to you.Most of the private lenders I have worked with were experienced real estate investors themselves with excess cash they wanted to put to work. 

You should only consider switching when your current software has a significant flaw or lacks features that force you to spend excessive time on workarounds.

BUT, does it lower cost of the burger, the bun, fuel to run the stove, wages of cooks to cook the burgers.....