That would depend on their long-term plans to stay in the home or are they considering a move or upgrade within several years. Also, are they wanting peace of mind with a battery backup for power outages, short or long-term?

Panel sizes vary so that is difficult to put an exact amount hoverer the panels rated wattage converts approx.. 82% to useable kw power. 

They do however, production would be much less than if they were in full sun.

No. They need uv or direct sunlight.

Most manufacturers warranty their panels for up to 25 years. However, with time the panel’s cells will degrade and produce less energy or just become less efficient. I am told the panel should last up to 40 years based on the site conditions.

Depending on the efficiency of you’re a/c equipment, some units are slow to start and have almost no inrush power spike to start the compressor, with that style it would say yes, overall load needs would have to be calculated.  If you have dated equipment, an upgrade may be required to achieve that.