Light fascia, a not quite white, but very light colour that matches the yellow house - maybe the colour on the knobs on the platform. Same light colour for the posts & rails of the deck for all except the very top hand rail leave that grey. Like the first picture in the comments. Paint the end board on the bottom stair platform the same colour as the house. Grey stairs perhaps. Leave knobs light.

The grey on the western wall looks dark and purplish on my monitor. It may come over as too imposing and monolithic on the southern face. If you're sticking with the grey palette then a warmer tone would suit the sandstone better. Does Dulux have a colour palette recommendation that includes your Berkshire White plus a grey? Check online or in store pamphlets. But, for such a big, expensive, and impactful paint job I would actually be tempted to get a colour consultant. You're not just repainting a loungeroom wall if it doesn't work!

There are lots of paint manufacturers apart from Dulux, and hundreds of whites that it could be. Unfortunately the natural light in the photo, the type of camera, any photo editing, and the adjustments on your computer screen make it impossible for anybody to say with any accuracy what the colour may be. The only way to find the right white is to get samples and make your own judgement on site. I always think that Perth light seems stonger and brighter than Sydney light - possibly due to Sydney's airborne pollution in the inner city? There are lots of online resources by various paint manufacturers about choosing the right white, but don't make selections from an online digital image as it won't be accurate. Best of luck, Dr Retro of Dr Retro House Calls

@dreamer yes I was thinking a simple timber balustrade would look better than a more modern one. we are planing on putting a covered deck off the back with a similar balustrade too. @fianou Luca I love fixed upper. They were the reason we bought this house as I could see the potential. it is much harder than it looks go bring a look all together. I was contemplating painting the brick lighter like a wash but to scared to vomit incase it looks terrible and it is an expensive job to do. I was even thinking of putting shutters on the windows downstairs to give the front some texture