Your design scheme has a very traditional European feel. I would continue with this and look at a couple of Louis chairs. The link I've attached shows one with a mix of rattan with an upholstered seat cushion. You can also get them with an upholstered back and arms. However I quite like the rattan for contrast so it's not too matchy matchy with your sofas. http://www.canalside.com.au/productimage.php?product_id=115&current_image=1 You could then add a scatter cushion to the chair. Have you thought about also adding a couple of scatters cushions to each sofa, in a silk or silk like fabric. Check out Kaz's Samara range. Not sure what colour to recommend as I can't see your wall colour clearly but black goes with most colours. Oskuee's rugs are lovely, just make sure the colour ties in with your colour scheme. As you have plenty of dark timber in the room already, consider a glass and metal coffee table and lamp tables in a gold finish. Gorgeous crystal or mirrored table lamps and an ornate gold framed mirror over either the chairs or the sofa to finish off the room.

It's a pretty substantial beam so a 10-12mm hole for a bolt through the flange will have little if any affect. Certainly no worse than cutting holes through the web for running of plumbing and electrical's, which is where the majority of a beams strength is. We secure cabling to steel beams with holes drilled into it so shouldn't be an issue. The difficult part may be drilling the hole (for some). It probably the hardest one to do.... It's overhead and it's steel, so a nice sharp drill bit is definitely needed as is safety glasses, ladder, etc. The swarf (drilled metal) is sharp as hell and usually hot during the drilling so again safety first. Sweep up any remains as it cut's little bare feet like razor blades! I dread drilling overhead with a handheld electric drill and the bigger the drill bit the worse it is as they can grab when almost all the way through the hole.....and I've done it thousand's of times......

Maybe try Asian/Balinese style business or look at pinterest: that will give you idea that you could take to a tradesman and get a quote on bespoke or if you have a male that is very handy some great ideas on that link. https://www.pinterest.com.au/pin/419679259009258301/

Flip up and bi-fold are indeed "all or nothing" options that can be tricky to screen too. Both also rely heavily on well-engineered operating mechanisms and as such come with increased potential for problems. I once stayed in a house on North Stradbroke Island which had a large flip up gas strut supported timber framed window over the north facing kitchen sink with views to Cape Moreton. (I now wish I had a photo to share, but sadly I was too much in the moment to take any.) Standing at the sink, looking north over the Coral Sea with Humpback whales breaching in the distance was one of those forever moments. Plus, our elevated situation seemed to reduce the number of insects that came through the unscreenable window. In that case I wouldn't have compromised on spending to get that window out of the way. For just about every other context I would opt for a less complex, less costly, screenable, servery style window.