My question is how to use this to ensure my equipment is sized correctly. I plan on using heat pumps to cool my house in the summer and heat my house down to 35-40 degrees. Once it's too cold for the heat pumps i plan on having back up propane furnaces kick in.

1st floor heating/cooling (hvac 1) is 43,393 btu and 2.1 ton
2nd floor heating/cooling (hvac 2) is 35,067 btu and 1.5 ton

How do I use the cooling tonnes to determine appropriate sizing of the heat pumps?
Also what size propane furnace would I get, would a variable furnace change anything? I'm guessing something like:
HVAC 1
Goodman GMVC950704CX
69,000/48,000 BTU Furnace, 95% Efficiency, 2-Stage Burner, 1,600 CFM Variable Speed Blower, Upflow/Horizontal Flow Application

Hvac 2
Goodman GMVC950453BX
46,000/32,000 BTU Furnace, 95% Efficiency, 2-Stage Burner, 1,200 CFM Variable Speed Blower, Upflow/Horizontal Flow Application

Am I on the right track?