Looking For help sizing my Mini split

I did a manual J I don’t know if I did it right please see attachment.
Total Heat load 27000 BTU Cooling load 14000BTU
I wasn’t able to add all the details of my house in the manual J
Zone 6  Iowa
We have R12 Zip Panel R21 open cell in walls R33 total
r60 cathedral Celling 
and R12 under slab
No blower door test but I have done my best and am well aware of the benefits of a tight house.

This is a 2 level home

level one: 2 stall garage and utility room 900Sf  TOTAL HEAT BTU 11900
      Garage load Heat 10,100BTU 264 CFM
      Utility heat 1800Btu 19CFM

Level 2: Living area  TOTAL HEAT BTU 15000
      Main / kitchen 7800Btu 194 CFM
      Bedroom 2400Btu 61 CFM
      Bath 1600Btu 33CFM
      Stairwell open to the main living area 3200BTU68CFM

was Quoted a  Daikin 36k Btu mini split with one 18k head for the garage and one 18k Duct unit upstairs

I feel like I could get away with there 24k Btu unit and have a 15k unit upstairs and a 12k Down

Right now I am using a 17k bth electric heater for both the down and upstairs and it keeps it very warm  “although outdoor temps right now are 20f” this I feel is giving me skepticism of the manual J report.

Any help very welcome