Mini splits require cleaning of the indoor unit, preferred once a year.
That's a feature, not a bug.
I keep my water heater at the low / average temp setting to minimize consumption (I can use the faucet at max hot without getting burned) and shower at the gym when I can so I don't believe that is large gas consumer.
I don't know what temperature you are setting the hot water storage tank to heat to but if it's the same as the temperature you use at the faucet then that's quite possibly dangerously low.
Water storage heaters should be set to heat water to a minimum of ~60°C (~140 °F) with reasonable frequency (a few times per week) to ensure legionella does not get a chance to grow. It is a lethal bacteria.
In any case, with hot water storage the energy consumption is dictated by how much hot water you consume, not so much by the temperature of the water in the tank.
All that reducing the thermostat set point does is slightly decrease daily heat losses, but for a well insulated tank that reduction in heat loss is very small. If the tank's water is hotter, you use less of it as more cold is mixed into the supply to reach the preferred use temperature. Indeed lifting the thermostat set point is a way to store more energy in your tank and effectively increase its hot water supply capacity.
How much energy do you use to heat water?
I know the question wasn't directed at me but this is our quarterly average grid energy imports for water heating for the past seven years. We have a 315 litre (83 US gallons) electric resistive water heater supplying a two person household. It was until recently powered via a dedicated off-peak grid supply circuit.
Some gradual reduction in hot water consumption over the years (always good to work on consumption reduction, not just supply) then last year I installed a smart PV diverter to operate on one phase of our grid-tied PV system to heat our water in preference to importing energy from the grid. It adjusts the power delivered to the resistive element to match excess solar PV supply so as to avoid importing energy from the grid.
If necessary (e.g. if we have a run of poor solar PV production), it can also boost from the grid off-peak supply but it's just not been required since I disabled that option in October. After first installing it I used the mode allowing it to self-boost from off-peak but it was a little too keen to boost at times when waiting until the next day to top up from solar PV would have been fine - that's the point of larger storage capacity for hot water - it's a thermal battery which can ride through a poor day of production. Can see the results in recent quarters.
Here off-peak electricity is more expensive than what we get for exporting excess energy to the grid. About 8 c/kWh (US 5.4c/kWh) more. So using our own excess supply makes sense (and more so for regular supply when the tariff differential is 15-29 c/kWh depending on time of day tariff).
I will see how it goes this Winter but I expect we'll all but eliminate the need for grid energy for heating water and will have increased self-consumption of our excess PV output by ~5 kWh/day.
Being where we are, the incoming cold water temperature is probably ~15 °C, so it doesn't have to work as hard as units in colder climates. Tank is inside our laundry. Hot water storage tanks in Australia are often outdoors.