Cavity wall insulation not possible with 9" solid walls. Waste heat from filament lamps heats the house, so no point in low energy light bulbs (CFLs) unless outside - or in my off-grid summer house with its own solar panel and battery. CFLs *not* reliable in my experience - overall cost (purchase/running/disposal) is higher than with filament types.
Have inverter installed in an accessible location in case of problems (none so far, but they are stated to have a 10-year life). Mine is in an airing cupboard so the waste heat (they're about 90% efficient converting DC to AC) does something useful. Also, ensure it's mounted on a solid wall (they're heavy) - hum is not a problem despite the cupboard being in a bedroom. Find out in advance how much space the inverter needs - download installation diagrams etc. from the manufacturer's website. I had to alter some pipe layout and relocate the solar thermal control box before the installers came so I could accommodate it.