a) reverse cycle AC with inverter
is the oz name or branding heat pump but with a DC motor drive that
can do variable speed. Practically continuiously variable speed. The
new model that I look at a EER or FEER or COP.... but I mean 1kw
electricity can cool 4kw or heat 4 kw. vs my old 6.5 kw LG box (come
with the house) which is ~2.5.
The big ducted one seems to have less efficiency. or more old models
are still hanging around.
I have very little idea of how well does these heat pump work. I don't
know whether I should go for a big system or multiple of small units
b) I have a central evaporative cooling in the last house also in
Melbourne. Most of the time, I am running it with the water off. More
of less running as the house exhaust fan like you have described. I
think the average humidity is ~40%.
It seems that which other path I choose, put a reflective film on the
glass of the window is a good bet.