I have an open plan home too but mine looks a bit larger. I would open the space instead of trying to make rooms using the furniture. If there is no other wall, you could put your couch where the tv is and place the TV on a smaller table on an angle where your gas connection is. I would also lighten and brighten the furnishings with chair covers, cushions and maybe even a stretchy lighter couch cover (good too as you can wash so keep fabric on couch clean). I would add some drama and frame the windows with ceiling to floor side drapes leaving the rest for natural light. You can easily do yourself with some cheap cotton fabric and some curtain hardware (as they are not functional, you just need to hang and drape on sides). Id turn your dining table the other way and get some nice stuff happening on your fence outside to draw the eye to the out doors. You could grow creepers, ivy or hang some trailing plants in a row from the fence. There are some great pots that hook onto the top of fences for this so no drilling required. You could also combine fake trails with real until the real ones grow for instant green. Amazon have cheap fake trailing ivy etc. Or, Put some ficus or other trees in pots along the fence. Id repeat some green indoors too ie a pot here and there in corners as you have so much light. Id also get a washable rug to cosy up the tiles and make it look less stark ie one you can throw in the washing machine! I just bought a soft one from target for $25! Alternatively, buy an outdoor plastic one as they can be hosed. I use one of those too and as I have pets, tits great. They have some cool designs too. Chair covers will update your dining chairs and are cheap on sale at places like spotlight and kmart. Lastly, Id look on gumtree for some cool lamps or a hanging light for your dining area. You can be modern but always balance with some natural elements like wood so maybe a wood based lamp or a couple of wooden ornaments. :)

Your home looks lovely. Ideas that come to mind for your 'dining' room include a sewing room, craft room, reading nook or children's playroom with a day bed but any of those ideas will only work if you have use for them. I know you have said you don't want another sitting room but my instinct would be a pair of wicker chairs, a jute mat, a small side table and some indoor greenery - essentially making a summer sitting room/reading room. With regards to your coffee table, perhaps include some texture. Either a mat under the bowl or fill the bowl with brush balls or something similar. Otherwise it appears to work well with your other furnishings and style.

Got two options 1) have dining area in front of kitchen in closed off section or 2) have it flow out by the doors. 1) have dinning table in front of kitchen in closed section. Have sideboard it like running under the window. Will allow for storage and display. Pictures on the wall of course. And bar stools off the kitchen bench for homework/Sunday breakfasts etc 2) have it by doors so lounge is more snug. Have side board or entertainment unit run down left hand wall with tv point on it. Have L shape if you fancy with return running under the window. A rug centre filling the centre of the L. A low profile occasional armchair off the end of the kitchen bench. Could add a small square coffee table too. Remember curtain rod to go as close to ceiling and hand to floor curtains to create height illusion. Good luck

Looking at your plans, your approx width of the dining room space is 2770mm X 4400mm length, allowing for walk ways. This space would be better for a 1800mm - 2100mm length, rectangular table, in my opinion, not a round table. also your plans are showing a gas point, exactly where you also have the drawing of your sofa in the first photo posted. The gas point will be difficult to use if your lounge is going in that space.