Hi Yooou,
It is an interesting project. I've actually worked with a few other customers on similar art/furniture projects, some with great success.
Of course, it really depends on the inherent strength of your design and exactly how you implement the use of the carbon fibre but my initial feelings are that a single layer of carbon fibre braid would not be strong enough to form an integral part of the loadbearing structure of a chair/bench. Doubled-up or even trippled up then I expect it would be a single sleeve of 20mm braid only has a wall thickness equivelent to a 318g carbon cloth. There really isn't much in composites that you can make with a single layer of carbon 300g cloth.
The twisted-tow type projects (like the first link you included) normally use quite a thick tow of carbon fibre, I believe something like 3 layers of the 'spread-tow' (removed from a spread tow fabric like our
15mm Spread Tow Plain Weave Carbon Fibre). The 3 tows can be stacked on top of eachother and then lighty misted used activated epoxy resin sprayed lightly onto them to make a loose bound carbon fibre strip (still very flexible and 'dry', but held together enough to be useable) which is then wrapped around the form and then wet thoroughly through using epoxy before it's all cured and then the sacrificial core removed).
Like Matthieu says, the essential thing with this kind of art/experimental composites is to to small samples and test the performance/results until you get the results you need.
I hope this helps and look forward to working with you.
Best regards, Matt
Matt StathamEasy Composites / Carbon Mods - Technical Sales