tldr; You will likely be relying on electric heat during winter months in combination with the heat pump because of the diminishing capacity of the heat pump during winter. during shoulder seasons you will likely be able to rely only on the heat pump. I am assuming you have a minimum of 9.6kw heat strips.
Capacity and efficiency diminishing returns occur all the way down to -10f. Note: Efficiency is always better than running the electric resistance heat in the air handler. so always max out the unit before the resistance coils (heat strips) turn on.
https://www.alpinehomeair.com/related/RT6214005R6%202.2014.pdfPage 37. bottom left. COP = Coefficient of performance, higher is better. and I'm fairly certain the btuh should be kbtuh (Typo?).
For sizing,
http://www.loadcalc.net/load.phpThe Manual J calculation is what I use for homes, but my knowledge for sqft based is on cooling down here, so I can't give you a btu/sqft to just go with.
http://cms.ashrae.biz/weatherdata/STATIONS/716280_s.pdfThis is your design conditions. in short, your location goes to negative 21 C. (~ -6F) So your heat pump should be able to operate down to minimum temperatures, unless a cold snap hits hard, but likelihood of that is less than 1% of the year. The question is would it be able to heat your home up enough with only 15kbtu of heat.
Gut check, your sizing is fine. as far as actual installation and compatibility I'm not your man. I'm only the engineering side of that equation.