You should be able to do three panels in those windows up into that arch with horizontal louvers and fully functional. Your shutter maker just needs to line vertical posts up where you have vertical mullions! giving that center shutter something to hinge to. Here are a couple of similar windows I have done. It's a partial arch but it's the same concept with yours

I have miles of decking at two houses. All timber when put in the Australian sun will suffer. When building our beach house we decided to go for Spotted Gum and let it grey. Why fight it? We applied Cutek, and will on a regular basis. At our main house we have lots of Merabu or Quilla. Will not grey the same, and leaches lots of red stain. Cheap, but would not use again. What ever you use, use a good quality oil that seeps deep into the wood not a traditional stain/or top finishing product.

Merbau is an imported hardwood apparently from Indonesian 'sustainable forest's'.... I'd stick with local hardwood's as you will know well truly that they are 'sustainable forest's'..... It's only a few bob more so may as well support aussie job's as well as the environmental factor's such as transportation. Tallowwood is a good outdoor timber but so is spotted gum and ironbark. Just come down to cost for me as all aussie timber is world standard quality. You could put fibre cement sheet on top of rafters then colorbond over. Lot of options to choose from, plywood, t&g timber as well as the fibre cement sheet. Depend's on the 'look' you're after, budget, etc.

Hi monicafowler96 There are pros and cons for either a solid hardwood timber flooring or a quality engineered flooring. Solid will give you a longer life span with more times it can be sanded and refinished but ususally more expensive to lay and finish in the desired finish. A roasted solid timber is a good option if you want a dark floor- also makes it harder and colour penetrates right through. Make sure the timber is acclimatised before laying to minimise movement (shrinkage and expansion) or cupping can occur. A quality engineered flooring with a thick wear layer is often chosen because it still gives you 2-3 sands. It comes prefinished so it's cost effective. Some are smoked so any scratches are minimal in appearance. Check out the Venture plank range from Havwoods for a product with a thick wear layer. https://www.havwoods.com.au/flooringsearch/engineered-timber-flooring/venture-plank Stay away from any of the thin or mdf backed products. Arena Venture plank pictured above Just a further thought- make sure you have alot of natural light if you want a very dark floor and they do require more cleaning as they show the dust. Best wishes