A colour called paperbark. It has green undertones so works with both the roof and windows, although will look nice against the garden too. Another is bushland, both are colourbond colours, and available in paint too.

You can borrow wallpaper books from suppliers and compare some you like by holding the samples up to your walls. Be sure to test how well they complement each other at different times of the day under different light conditions. I know it's hard to know for absolute certain how a particular wallpaper pattern will look on a large scale, but it's a place to start. And the people at the decorator stores will be happy to advise you.

there are some interesting putty grey colours in the knots of your floorboards. I reckon it would be worth holding some paint swatches up to the boards and see if you can find one that ties in with those driftwood tones in the timber . Then order a sample pot in a half or quarter strength version of the matching colour then see how it looks. Otherwise it is so hard to go with colours people have named, as every space has different light. If you are happy with the colour of the floor boards, let them guide your choice and you can't fail (as long as not too dark). :)

I can't quite follow what you mean by 'we must keep the red roof' ? Are you not painting it , or repainting in the same colour , or would you consider a different shade ? Personally , with the White Duck , I'd go for a bolder red roof , with black or charoal gutterings , stay with the crisp white windows and veranda uprights , and the end detailing on the roof , but the window sills I'd do the same red shade as the roof , and the deck a mid grey . Oh , and also , although its cliche'd , I'd do a 1 metre tall white picket fence and double gates in the crisp white , get rid of the wire mesh haha , so everything about the house and fence looks crisp and themed , but also 'period' .