We did exactly what you're talking about. Removed a forced air furnace and ductwork and installed mini splits. Overall, it's been great. We have Mitsubishi hyper heat which are rated down to -13. First winter we had only the heat pumps, and had no trouble. As a backup we got a wood stove insert this winter which is nice for lowering the electric bill, but not critical. It's time to ditch fossil fuels.