I use a pressure cleaner and carefully clean it. I have a relatively cheap Stihl pressure washer and I clean my timber fences with it, driveway, etc. and no chemical's are used.

I've coated many decks and the best advise I've been given is "leave it natural". Most timbers go grey after a few months and don't look too bad. If you want a bi-annual maintenance job the other bit of good advise I've had directly from the manufacturer is put down four coats minimum. The third and fourth coats won't use so much oil because they don't soak in. A very light sand between coats keeping in the direction of the grain is a good idea to retain a finish without wood grain or dust spoiling the final appearance. Two coats, no matter which brand or type of oil will last about a year in our sun.

Use spa and deck. But you can definitely oil it.

Hi Anna, with your lovely bushland setting my preference is stained finishes that allow the character of the substrate to show through, not paint which will obscure the substrate material. Stained finishes on outdoor timber will be easier to maintain over time too, as you can wash down and re-coat rather than having to sand back. In terms of prep, use an oxalic acid based wood cleaner (following the safety guidelines of course) and give it a good scrub. Don't use sand paper or a pressure cleaner. After the cleaner has restored the wood surface you can apply a penetrating oil finish - at least 2 coats - to enhance the natural colours. If adding a tint, I would look for something that will reflect the bushland tones, probably greys. A strong orange look will not complement the bush tones. For your slab area, I would just give it a good pressure clean then apply a clear sealer, maybe add some grey oxide if the concrete is too light. The aim is to retain some patina and avoid solid blocks of colour like pavement paint would achieve. Sealer will age more gracefully than paint too. All this is subjective of course, but to me working with the colours and textures of the bush is the way to go. Looking forward to seeing your "after" photos when it is done!