Luke, don't mess around with gum trees. As beautiful as they are, they are prone to falling suddenly and unexpectedly and that is one huge tree that could take out a couple of homes in the process. I've also found that if part of a tree dies, it can affect the balance of the rest of the tree so it becomes unstable even though it may look healthy. If an arborist says it needs to come down then I wouldn't waste time, you could void your insurance by not heeding advice. Do you need Council approval? Sometimes that can take a while to get.

Why don't you pick your cabinets first? Then get the wall colour paint matched to the cabinet. Way easier that way, and a guaranteed way to avoid the awful white clash. Vivid white is very stark.

Pandanus. We have a few in our yard.

i would also omit the clerestory windows as the focus should be from the inside looking out, keeping the fireplace central allows for symmetrical joinery and the couches can then be placed to allow for a walkway and cabinets/shelves along the bathroom wall and keeps through traffic from obstructing a view of the fire, TV and the pool....keeping in mind that the only time we ever look directly at the external wall so carefully is on the plans... in the real world we see the wall looking close up from ground level in the side yard or from across the street from an angle but a simple faux chimney added to the external wall could be enough interest and/or if there's space for attractive landscaping a tall window matching the main house and a glass door could add cross ventilation, late afternoon sun and interest viewed from inside and out but consider a wider landing, steps and perhaps a porch roof if the side door will be used regularly