I have a different model (2020 3813MS) And had the 3rd AC installed by a mobile rech and his helper. They got it on the roof just fine without a forklift. All wiring was already in place. Not sure if they put the breaker in the electrical panel or not. All 3 AC's are Coleman mach 15's, power saver version, one with the heat pump. I can run all 3 at the same time with no power issues.
One thing that helped A LOT when we lived in southern CA was a cover over the roof from
www.shaderv.com. With one of those covering the roof, I was able to keep the inside temperature below 80, even when it got to 110-115 outside