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.

Very light grey on all walls would be nice or white. Lighter colours like white tend to make spaces bigger and in ur case this needs to be done. The artwork on the weight bearing wall (in kitchen) needs to go as this draws ur eye to the wall . The railings on the stairs need to be painted (either colour of the walls or white)as this will help blend into the background and make the space look bigger.

To be a voice of dissent, have you considered soft greens or green-grey? I've got Baltic Pine floors, pine cabinetry, stainless steel appliances, and black tiles in a BRIGHT west-facing kitchen. I went with Taubmans Swiss Meadow double strength and it compliments all the different elements. If you don't want something "obviously" green, check out Taubmans Alpine Snow (double) - it seems to change colour in different light. It's a pale green in full daylight, but looks soft grey at night.

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' .