New Heat Pump Considerations.
My first thought would be, if you have the indoor real estate for a new air handler (if needed because of newer efficiency compatibility issues) I would go the split route and not try to change a duct system that we assume was designed and balanced for the floor plan.
You are in east TN and that is prime heat pump territory. Lots of 30-45 degree winter nights that will ultimately lower your utility bill as compared to your current AC unit. And if you have only the most common of insulation factors, I think 3 Ton is plenty for your neck of the woods.
If you are considering trying to utilize your current elec furnace and add a new outdoor HP, let us know the make, model and age of your existing indoor unit, as it may not (probably won't) be compatible.
Settle down! If you were that important, the city would give you lights and a siren for your car