We've been using a heat pump for just over a year, has cut the average electricity usage over a year in half (as measured 24/7 with an effergy engage power monitor) and it works great, we run from 5AM till 10AM, and again from 6PM till 11PM each day. the only extras are a geyser blanket and insulation on the pipes between the geyser and heat pump (Minimize losses while circulating water)
There is always hot water, with 5 people in the house and dishwasher also using hot water. However in winter, the heating times are a bit longer (2 hours to heat 250L from 15degrees to 60 degrees) but through the rest of the year it will do the same cycle in 45mins.
I would recommend looking into these.
I would also be interested in cooling the roof cavity in summer, perhaps even sucking the hot air out in the evening for bonus efficiency?