Hi---since you want to keep it bright and rich, I suggest Muted aqua/turquoise blue. Pics for inspiration-second pic the furniture and drapery hues would look great with the gold. Good Luck! Love the BOLD Yellow... :) [houzz=][houzz=][houzz=]

Sophisticated start. You could go with black and white photography, architectural pieces, art pieces- anything you love on the wall. Then, add pillows in the colors of the art work. If you want to stay more monochromatic, think in terms of textural interest, such as a shag area rug, pillows with seam detailing, etc.

Textured linen or with a subtle print wont date. Feature walls make a room smaller as they jump out ar you. Wouldnt recommend. Get some interesting art or craft. Pick up colour with accesories

For a pass through window to be very useful, it needs a surface to place items that are being passed through, that can be easily reached from both sides, or you would need to coordinate people inside and out to pass things, which isn't feasible. I would consider whether it will be used as a pass through, given the door is immediately beside it. A small breakfast bar that uses the window for a view can also be useful for a pass-through set-down surface. Make sure the window is large enough to give a line of sight from person to person so that it is easy to communicate between the spaces - along the lines of 'Could you grab another beer?' or, 'I forgot the sauce.' I would also make the pass-through window a little wider if you do have a seating area, so it looks big enough to be welcoming, or it will be less likely to be used. At 2.500 deep, the deck is not large enough for a comfortable outdoor dining area of more than a couple of people. You need 600mm for comfortable seating on each side of a table, plus the table width which will be 900-1200, and with this layout, you also need another 900 mm to allow access past this, to the pass through, the seating and to the steps down, and with the deck being above ground level, space for access beyond the seating on both sides of the table is a good idea. If there is a barrier, you can get away without it because chairs won't fall off the edge, but it does make things tight. That adds up to at least 3000-3500 and preferably more. You can make things work with a tighter space, with a compromise to fixed seating along the edge, and a narrow table.