First timer needs a little advice

I'm considering replacing my current forced air oil heat & AC on the second floor of my 1920 farm house with a Tri-Zone Mini Split Heat Pump System. Planned replacement is due to basement remodel require move of current duck work, planned partial second floor addition as well as HVAC contractor indicating current supply & return duckwork to 2nd floor not large enough to provide correct heat/cool. Current 2nd floor is only around 600 sf (3 bedrooms & bath) - planned addition will add another 500sf. Current oil heat works ok for 2nd floor (not great but ok) but AC does poor job during hot summer months - I'm forced to install a window AC. I have also added around 20 inches of blown insulation in the attic as well as installing ventulation in the attic. The forced air oil heat & current AC will continue to be used for basement and 1st floor.

My concerns is whether or not a Mini Split Heat Pump will be able to supply 60to 70 degree heat when the outside temp could get down to between 10 - 30 degrees on average during the coldest winter months in Southern MD. I've read that the Mini Split Heat Pump System only works down to around 35 degrees.

Any poster/readers from the Washington DC or Maryland area that have the Mini Split Heat Pump system install - what do you recommend - how does your system work?