I want to be sure that I have adequate life insurance in place to cover the mortgage on my primary residence, as well as any rental property/s I may purchase so in the even I exit this mortal coil, my family can pay off any debt.The agent I spoke with tried to tell me, "good news... you can deduct this if you have a business..." but I'm not seeing that as the case.

If the budget allows I would stick in gas furnaces with A-coils.

Total repair range $150-400Range- I recommend coil top ranges over glass.

Our next rental is going to get a glass top range (the one in our house currently) and we're going back to one with coils.

As for the unit freezing up; I am a HVAC contractor and if the unit is installed with a blower size that matches the evaporator coil the unit will never freeze up.

If you are just swapping out a new FAU with furnace, condensor and evap coil and not touching any ductwork and don't have to replace line set and can use the existing electrical, you are looking at about $4500 or so for a 4ton unit.

Assuming it's steam with a domestic coil.

Mine was a heater coil with so much dirt and pet hair it looked like a shag carpet was draped over it. 

Do I truly need to replace the whole system, given that the inside coil and blower fan, in my view, doesn’t look too bad? 

Clean filters inside and a clean coil outside guarantee this.