I'm not an expert, but we have renovated a pool and made 1 big mistake. We had similar coping that formed a big hob all the way around (unlike yours). We leveled it out with paving (and then coated the pebblecrete with an epoxy sandstone-look product). The mistake? Part of the yard sloped down to the pool. Every time it rained.....all the sand, dirt and debris from down the side of my house and around the pool went straight into the pool. If we had our time over- we'd leave a small hob around the side of the pool where the land sloped down. Yours looks like it is on the downside of your house with some garden. The hob might be there for a reason.....as we learned.

Hi. Personally, I think spotted gum flooring would complement the merbau decking and vice versa. And spotted gum has tones that will complement your Tasmanian oak furniture. Some screenshots of both:

We would need to know sizes, preferred materials, locations, etc. the list goes on.... There is no standard cost for building works as it varies from job to job. Even ball park costing can have a lot variables. My suggestion would be contact a local designer and discuss the details with them. They can advise on costs, plans and documentation for approvals, etc.

First step would be outline what and why the railing and deck needs replacing , so that you ( or we ) don't repeat the mistakes . Like oklouise said , what is the front and rear deck made of ( sounds like they are concrete slabs , but just checking ) , what are the rails currently , do you know how solid the pillars are ( they look a different brick to the house , so may have been added later and/or have steel uprights in the middle , etc ) . The answers to those questions will give 'us' a base -- a concrete deck or two is harder to replace than wooden ones , same with steel poles imbedded in 2 metres of concrete etc . Just some general comments though -- what is the material between the 2 windows on the upstairs front ? And you say about not replacing the windows , but possibly changing the rear door ? Is that because of cost ? The brown frames will always date your house , but they are no where near as bad IMO as the yellow glass . Personally , that glass would be the very first thing I'd change ; 2nd thing would be doing charcoal on the gutters and garage doors ; THEN I'd update the decks and rails . Depending on what the fill panel between those 2 upstairs windows above the garage doors is made out of , maybe paint it off-white or charcoal -- add some interest in a subtle way . If you keep any part of the blue rails , paint them . Also look at some landscaping , a solid brick or maybe charcoal coloured concrete mailbox , charcoal stained fences -- but I still shiver at the yellow glass haha .