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.

I also have a window like that in our shower - it may, but doesn't normally get wet from the shower. I have put in a thin venetian blind in white (made from plastic) very cheap, under $5. I am in process of making an puffy austrian blind to hang above the window, for a bit of colour I am making it from a shower curtain). It will be there for looks, I may never pull it down. The venetian gives privacy and blocks the light a certain amount.

It looks to be the underside of a beautiful hardwood timber floor. It might be wise to consider whether a new ceiling with insulation for that upper floor is needed in winter. All white would look good for a crisp finish & some colour on the wall. I personally would look at the area as a whole project & what look you are after. It may be that to make it look finished against the house that some boxing around the top of the pillars & a flat panel roof (could be grooved timber panels that come in large sheets ready for staining or painting) will make it neat & finished.

I would look through the many images on this app under a heading like "cathedral ceilings " and find a picture or two that you like the feel of , then follow that design... The feel of the earthy wood ceiling and a stark painted white one is miles apart... Only you are going to know which one feels right for you.. For me I would keep the ceiling and floors wood , render the inside brick and then decorate... I love an earthy feel.. There is also real stone cladding you could cover brick with. Have fun :)